tying a timestamp system into an RP can be harder than merely using one that is tied to post headers. Especially when the RP isn't set in "our" world.

But the general rule to follow for implementing clear time into an RP is to have it simple and easy to understand. It'd be fun to make an RP that didn't operate on a 7 days/24 hours/60 minutes/60 seconds basis, but making a system that doesn't confuse the players is harder than you
'd think.