Hand range:
(1) high diamond + random feature (pair, straight draw, etc)
(2) made hand that can catch you (set, two pair)
(3) flush ... this is ~85% beating you
Since (1) is most likely, and you'd like to allow (1)+(2) to make a mistake against you (by calling with incorrect odds; rather than giving them a free card), I'd reraise the pot on the flop (fold to a reraise), and lead the turn (fold to a raise). If I get called on the turn, I'm probably done.
I note incidentally that UTG+1 raised exactly the pot on the flop, suggesting he's a decent player. I think this makes a high flush slightly less likely?
Oh poker2006, I sometimes post as soon as I arrive, either through error if I'm multi-tabling ... or simply because 1/2NL is just too juicy to miss even one hand

... not sure if that supports or contradicts your "early post=fish" argument?!
Edit: Last time I had JTs on a low monotone board against a blind, I got well and truly stacked against a Q high flush!