Been there and done that at JFK with a few airlines including Delta. 65 minutes is really tight, but for departures it may be okay if your first flight is absolutely on time. You'll have to hustle and walk a fairly long walk to reach the Delta international departures, but it's possible. But, coming back the 65 minutes simply won't cut it. Once again it's a long walk just to get to Customs & Immigration (this is huge airport), and I would estimate you'll need about an hour to reach that point and get through the busy work needed before heading off to the next gate. IMO minimum time for return flights back from SXM thru JFK is 90 minutes. Sorry!