If I remember correctly (but last time I did a stop over with award miles it was during the frequence Plus period) it is possible to do a stop over BUT only after an international leg.
If you where doing ATL-CDG-MAD as an example you can do a stop over in CDG.
in your case the ATL-NYC leg is domestic and therefore does not allow for a stop over in NYC.
In all cases if the transit is less than 24H then it is not considered as a stop over so your only solution would be to find good timing to try to be as close as possible to the 24h window or buy two separate award ticket