DNS TTL value question

Hello,

We had  CNAME it was pointing to Porduction and changed the DNS to DR and worked fine.  We have nameserver( resolver in both sides)
Once we changed the DNS back to  Production,  DR resolver was still pointed to DR site, but PROD resolver was pointing to PROD as we exptected.

our TTL value was set to solve to 24 hours.  After 24 hours it worked, but my question is that how come it worked right a way when changed from PROD to DR ?