MAN-NEW YORK TIMINGS.
But something timed around a 5-7pm departure from MAN Id have thought would be popular.
As DJ6 points out, this would not really work for pax connecting on in the US.
However, given the increase in capacity to New York and that flights appear to be well used, it would be interesting to know how much of the traffic is purely O&D, (or is p2p the correct term?).
For transfer pax going on to say the west coast, the 3 hour time difference does provide some help. Nevertheless, I would suggest the latest timing to connect to say SFO would be a 13.30 departure from MAN arriving New York about 16.15. Both United and American have flights to SFO from EWR/JFK at 18.30 for dates I checked in June, arriving 22.10. Later flights at around 20.30 arrive after midnight so hardly ideal.
Looking at summer schedules, it appears Delta's JFK flight from MAN is now later at 12.45 with a 15.25 arrival, so there is some spread of options from 09.25 UA and 10.15 AA.