This doesn't sound like it's the case in your situation, but I may be reading the numbers wrong, so here's my experience:

My mother-in-law once flew TLV-JFK-ATL, with the JFK-ATL departure time being >24hrs later than the time we got to the desk at TLV to drop off her bag, and they wouldn't check it through, even though it's on 1 ticket, etc.
Didn't matter much in this case since she had to pick it up at JFK customs anyway and recheck it, so they took care of it at the counter there. Unfortunately for your dad, he wouldn't have to pick it up in ATL if they had agreed to check it..