I get hardly anything by way of a proper 'crash' from 6-APB. Nothing like the crash from MDMA, Speed, Coke, you name it. It's a gentle up over a couple of hours to peak which last a good long time, 8-10 hours minimum for me, then a long slow slide over a further 8 hours maybe down to something close to base till I'm ready to sleep. It can take easily 16 hours plus for me to get to nodding off territory but sleep comes easily.
The only hangover as such is tiredeness the next day after being up so long. Had ~250mg 6-APB saturday night, finally crashing around 11pm sunday, up for work monday, fine at work, no problems, crashed out soon as I got home and slept till 3am before taking myself to bed, fine again today at work. There's none of the suicide tuesday type serotonin depletion I used to get with MDMA for instance.
Having said all that I'm not one of those who gets massive amounts of euphoria or stimulation from it, finding it very subtle. Some compare it to MDMA in terms of both which I can't even begin to understand, but I suspect the higher you go with it the more you'd get in the way of a come-down.