diff --git a/scripts/tests/external-rpc-checks/.env b/scripts/tests/external-rpc-checks/.env
index c4eef04913a..84ddafc20d0 100644
--- a/scripts/tests/external-rpc-checks/.env
+++ b/scripts/tests/external-rpc-checks/.env
@@ -3,4 +3,3 @@ FOREST_IMAGE=ghcr.io/chainsafe/forest:edge-fat
 FOREST_RPC_PORT=2345
 FOREST_HEALTHZ_RPC_PORT=2346
 FOREST_CHAIN=calibnet
-FOREST_CHECK_EPOCHS=1000
diff --git a/scripts/tests/external-rpc-checks/docker-compose.yaml b/scripts/tests/external-rpc-checks/docker-compose.yaml
index 35e9c5d6cd2..ef54472d46f 100644
--- a/scripts/tests/external-rpc-checks/docker-compose.yaml
+++ b/scripts/tests/external-rpc-checks/docker-compose.yaml
@@ -18,7 +18,6 @@ services:
     entrypoint: ["ruby", "/resolve.rb"]
     environment:
       - FOREST_CHAIN=${FOREST_CHAIN}
-      - FOREST_CHECK_EPOCHS=${FOREST_CHECK_EPOCHS}
 
   init:
     <<: *forest-service
@@ -33,6 +32,7 @@ services:
     environment:
       - FOREST_PATH=/data
       - FOREST_CHAIN_INDEXER_ENABLED=1
+      - FULLNODE_API_INFO=/ip4/127.0.0.1/tcp/${FOREST_RPC_PORT}/http
     command:
       - --chain=${FOREST_CHAIN}
       - --encrypt-keystore=false
@@ -47,6 +47,7 @@ services:
           "forest-cli",
           "healthcheck",
           "live",
+          "--wait",
           "--healthcheck-port",
           "${FOREST_HEALTHZ_RPC_PORT}",
         ]
diff --git a/scripts/tests/external-rpc-checks/resolve.rb b/scripts/tests/external-rpc-checks/resolve.rb
index 1efd8f5a86e..de5121039af 100644
--- a/scripts/tests/external-rpc-checks/resolve.rb
+++ b/scripts/tests/external-rpc-checks/resolve.rb
@@ -1,32 +1,17 @@
 # frozen_string_literal: true
 
-# Picks the ${FOREST_CHAIN} snapshot published DAYS_AGO days ago (UTC), by the date in its name,
-# and records under /data what the rest of the harness needs: its URL, its head epoch, and the
-# chain plus the ${FOREST_CHECK_EPOCHS}-epoch range the checks cover.
-# Runs in the checks image, which has Ruby, so the Forest image needs no curl.
+# Picks the newest ${FOREST_CHAIN} snapshot whose head lies within the first 2000 epochs of
+# the UTC day: it holds the state the backfill needs to reach the day's start,
+# and the node syncs the rest. Writes its URL, head epoch and the day's epoch range under /data.
 
 require 'date'
 require 'json'
 require 'net/http'
 
-# Compose passes an unset host variable through as an empty string, which `ENV.fetch` accepts.
-def env(name)
-  value = ENV[name].to_s
-  abort "#{name} is not set" if value.empty?
-
-  value
-end
-
-def env_int(name)
-  Integer(env(name))
-rescue ArgumentError => e
-  abort e.message
-end
-
-chain = env('FOREST_CHAIN')
-epochs = env_int('FOREST_CHECK_EPOCHS')
-days_ago = env_int('DAYS_AGO')
-LIST = URI("https://forest-archive.chainsafe.dev/list/#{chain}/latest-v2?format=json")
+SECONDS_IN_EPOCH = 30
+EPOCHS_IN_DAY = 2880
+SNAPSHOT_DEPTH = 2000
+GENESIS = { 'calibnet' => 1_667_326_380, 'mainnet' => 1_598_306_400 }.freeze
 
 def fetch(uri, attempts: 3)
   reason = nil
@@ -42,13 +27,27 @@ def fetch(uri, attempts: 3)
   abort "failed to fetch #{uri} after #{attempts} attempts: #{reason}"
 end
 
-day = (Time.now.utc.to_date - days_ago).iso8601
-urls = JSON.parse(fetch(LIST))['items'].map { |item| item['url'] }
-url = urls.find { |candidate| candidate.include?("_#{day}_") }
-abort "no #{chain} snapshot published for #{day}" if url.nil?
-epoch = Integer(url[/_height_(\d+)/, 1])
+chain = ENV.fetch('FOREST_CHAIN')
+days_ago = Integer(ENV.fetch('DAYS_AGO'))
+genesis = GENESIS.fetch(chain) { abort "no genesis timestamp for #{chain}" }
+
+day = Time.now.utc.to_date - days_ago
+start = (Time.utc(day.year, day.month, day.day).to_i - genesis) / SECONDS_IN_EPOCH
+finish = start + EPOCHS_IN_DAY - 1
+
+list = URI("https://forest-archive.chainsafe.dev/list/#{chain}/latest-v2?format=json")
+snapshots = JSON.parse(fetch(list))['items'].filter_map do |item|
+  height = item['url'][/_height_(\d+)/, 1]
+  [item['url'], Integer(height)] if height
+end
+reachable = start...start + SNAPSHOT_DEPTH
+url, epoch = snapshots.select { |_, height| reachable.cover?(height) }.max_by(&:last)
+if url.nil?
+  warn "no #{chain} snapshot heads within the first #{SNAPSHOT_DEPTH} epochs of #{day.iso8601}"
+  exit 2
+end
 
 File.write('/data/snapshot-url', "#{url}\n")
 File.write('/data/snapshot-epoch', "#{epoch}\n")
-File.write('/data/check-target', "#{chain} #{epoch - epochs} #{epoch - 1}\n")
-puts "#{chain} snapshot for #{day}: #{url}"
+File.write('/data/check-target', "#{chain} #{start} #{finish}\n")
+puts "#{chain} #{day.iso8601} is epochs #{start}..#{finish}; snapshot at #{epoch}: #{url}"
diff --git a/scripts/tests/external-rpc-checks/setup.sh b/scripts/tests/external-rpc-checks/setup.sh
index 340f7ff5ca3..24e4df838eb 100755
--- a/scripts/tests/external-rpc-checks/setup.sh
+++ b/scripts/tests/external-rpc-checks/setup.sh
@@ -10,36 +10,59 @@ pushd "${PARENT_PATH}"
 # This should not be needed in GH. It is useful for running locally.
 docker compose down --remove-orphans --volumes
 
-# The dataset publishes each UTC day's archives some time the next morning, so
-# yesterday's may not exist yet. Try yesterday's snapshot first, and the day
-# before if the dataset has no data for it.
-for days_ago in 1 2; do
-  docker compose run --rm --env DAYS_AGO="${days_ago}" resolve
-  CHECK_TARGET="$(docker compose run --rm --no-TTY --entrypoint cat resolve /data/check-target)"
+# Resolves the snapshot and probes the dataset for DAYS_AGO.
+# Sets CHAIN, START and END on success.
+# Returns 2 on failure
+check_day() {
+  local status=0
+  docker compose run --rm --env DAYS_AGO="$1" resolve || status=$?
+  case ${status} in
+    0) ;;
+    2)
+      echo "no snapshot covers the day $1 day(s) ago"
+      return 2
+      ;;
+    *)
+      echo "resolve failed for the day $1 day(s) ago with status ${status}"
+      exit "${status}"
+      ;;
+  esac
+
+  CHECK_TARGET="$(docker compose run --rm --entrypoint cat resolve /data/check-target)"
   read -r CHAIN START END <<< "${CHECK_TARGET}"
   [[ -n ${CHAIN} && ${START} =~ ^[0-9]+$ && ${END} =~ ^[0-9]+$ ]] || {
     echo "resolve did not report a usable chain and epoch range: ${CHECK_TARGET}"
     exit 1
   }
 
-  probe=0
-  docker compose run --rm rpc-checks --probe --network "${CHAIN}" "${START}" "${END}" || probe=$?
-  case ${probe} in
-    0) break ;;
-    2) echo "the dataset has not published that day yet" ;;
-    *) exit "${probe}" ;;
+  docker compose run --rm rpc-checks --probe --network "${CHAIN}" "${START}" "${END}" || status=$?
+  case ${status} in
+    0) ;;
+    2)
+      echo "the dataset has not published the day $1 day(s) ago yet"
+      return 2
+      ;;
+    *)
+      echo "the dataset probe failed for ${CHAIN} ${START}..${END}"
+      exit "${status}"
+      ;;
   esac
-done
-[[ ${probe} -eq 0 ]] || {
-  echo "the dataset has published neither yesterday nor the day before; raise it with its maintainer"
-  exit 1
 }
 
+# Tries to fetch latest available archive dataset (from yesterday)
+# if not available lookup an archive dataset before yesterday
+# if nothing is available then fail
+check_day 1 || check_day 2
+
 # Imports the snapshot and back-fills the index.
 docker compose run --rm init
 
 docker compose up --detach --wait forest
 
+# Syncs the rest till reach END.
+docker compose exec forest \
+  timeout 30m forest-cli sync wait --target "$((END + 1))" > /dev/null
+
 docker compose run --rm verify "${START}" "${END}"
 
 docker compose run --rm rpc-checks "${START}" "${END}"
diff --git a/scripts/tests/external-rpc-checks/verify.rb b/scripts/tests/external-rpc-checks/verify.rb
index 567ba308c91..57987db1c5f 100644
--- a/scripts/tests/external-rpc-checks/verify.rb
+++ b/scripts/tests/external-rpc-checks/verify.rb
@@ -1,7 +1,6 @@
 # frozen_string_literal: true
 
-# Confirms the back-fill indexed the epochs the checks query. Runs in a container
-# so the node's RPC port never has to be published.
+# Confirms the node indexed the epochs the checks query.
 
 require 'json'
 require 'net/http'