I read in a Stephen LaBerge book about a guy who dreamt he was in the French Revolution and was put on trial. His dream went through the entire trial process, complete with sentencing to execution, and "the next day" he was put under the guillotine, only to wake up a second before the blade hit his neck. When he woke up he realized the headboard of his bed had fallen onto his neck, like a guillotine blade would, and that was the reason he woke up. So by that logic, the dream would have had to take place over a fraction of a second, despite it feeling like several days. I think the guy this happened to was Saint-Denys or somebody, but I'd have to recheck the book.
I've had a time-dilated dream too, so I know he's not bullshitting, at least not totally. Also, taking mushrooms can stretch time out quite a bit. It's weird to be listening to a 3 minute song and experiencing it as 3 hours, but without the audio going any slower or changing in any describable way.
Seven years is a long, long time though. Wouldn't you get bored enough to quit after seven years of walking on the ocean bottom? Or at least, over those seven years, wouldn't something notable happen in between beginning and finding a portal to hell?