I think is all depend from conditions, I was waiting over two weeks with both upstream and downstream capped and where on upstream fastpatch kicked after three days on downstream didn't for over 15 days. I decided to remove cap from upstream as higher snr due to cap cause strange high snr on u0 band (if I good remember). After 3 days with cap from 69 to 58 on downstream only, fastpatch kicked in on downstream. I personally think that time doesn't matter, I have like 300k fec errors in over 15 days (no other errirs at all) and dlm didn't give me fastpatch, so there must be other conditions like snr on all bands which tell dlm if something else may be wrong with line, just basically on my own experience.