How long should I keep a response in cache?

[renanbr]

The documentation says

Cache data so you don't request the same data over and over again.

I'm trying to implement it, but I don't know the TTL value I should use. I tried find some tips in responses header, then I noticed that headers like Cache-Control and Expires are missing.

E.g. https://api.crossref.org/works?filter=has-full-text:true&mailto=GroovyBib@example.org

HTTP/1.1 200 OK
Content-Type: application/json;charset=UTF-8
Vary: Accept
Access-Control-Allow-Origin: *
Access-Control-Allow-Headers: X-Requested-With
Content-Length: 40723
Server: http-kit
Date: Thu, 09 Nov 2017 00:43:41 GMT
X-Rate-Limit-Limit: 50
X-Rate-Limit-Interval: 1s
Connection: close

Then I still don't know for how long I should keep data in cache.

[renanbr]

I mean I was expecting https://tools.ietf.org/html/rfc7234 compliance or at least a recommended TTL