This is such a tricky topic and something that is such a pet peeve of mine. When one character can take his leave of two other characters, go shopping and stop for a cup of coffee while two others are having a conversation and then the third returns to interrupt said conversation that was less than five minutes IC is enough to make me batty. I've tried time stamps and they worked ok, As a GM I was sort of the control time and seeing it at the top of my posts made people more aware of the passage of time. But we still ended up with people in a collab that took maybe five minutes IC having to sit out over a month OOC because the meeting they were supposed to attend IC took so long. It got frustrating for all.
If you think about it, without time skips, IC time passes so slowly OOC. People take days to post, conversations that could be minutes IC take weeks OOC. I think that's one of the many reasons people wind up with Love at first sight and other awkward plot progressions. Just think about reading a novel at the pace most RPs move. But if people are having fun *shrugs*
I think my preferred method is just lots of OOC communication about time passage and everyone trying to be on the same page. And maybe, just a few timestamps... just a few.