7~10 min seem normal to me. If thermostat is stuck open, I would think it takes heck of a lot more then 7~10 min to worm up if worm up at all.
when thermostat on my MR2 stuck open, it took like 20 min of idlein' for needle to move at all, but then as soon as you move, needle went down. But mine was compleatly stuck open tho..