I don't think 7 days is too long, by any means! Some folks flush for 2 weeks. Flushing isn't going to do anything to the terpenes. I think one prolly could flush too long, but I don't know what "too long" would be--I guess all the trichomes would turn amber, and you'd end up with total sedative effect. I think 7-10 days is a good flush. On my first grow, I thought you only flushed hydroponics for 2-3 days, so that's what I did. Now I have no way to prove it, but the weed from the 1st grow is good weed, only harsher and darker ash. I flushed the second grow for a full 7 days, and like I wrote above, it's smoother and ash is whiter.
It's an art, right? Knowing what percentage of the trichomes are milky, starting the flush, letting the trichomes continue getting milky during flush, and then harvest. I think most of us get so impatient that we want to rush at the end instead of taking our time w/ the trichomes and the flush.