I grow Harglow, which is reasonably hardy for the northeast, at least down to Z 6. It blooms almost a week later than most here. This has not saved the crop for me after about 8 years because the hard frosts have come outside that window, which is often the case with later blooming cultivars or cultivars that are a few degrees more bud hardy- most years it isn't enough to make a difference. Apricots are by far my most fragile trees, incidentally. Sometimes I can't even pinpoint why the fail on a given site.
[NAFEX] later blooming cots,
Alan Haigh, 04/12/2008