I like the idea of the time only being deducable from physical things within the game, like Ultima-style sundials, or just intuiting it from NPC behaviour. The weather conditions should be pretty obvious from on-screen effects, to be honest.
I'd rather have a time display. I know it's not especially realistic in a medieval setting, but there are some issues where gameplay trumps realism, especially if quests etc. are going to be affected by NPC schedules.
