The standard rule, going back to B/X I think, is to roll 1d6 to check for random ( on a 1) encounters every other turn. Instead, I’ve been rolling 1d12 (still just on a 1) every turn because that should create the same overall frequency while not arbitrarily ensuring that the time between random encounters is always a multiple of 20 minutes.
But I also realize that sometimes the old rules do things a certain way for reasons that aren’t obvious. Can anyone think of an advantage to only rolling for an encounters on even numbered turns? Maybe an administrative reason?