I honestly think a global time limit for an open world RPG (or really any RPG in general) seems like an absolutely awful idea, unless the game is either completely built around this gimmick like Majoras Mask, or it's something absolutely crucial to the main story like the water running out in Vault 13 in Fallout 1.
Basically, this would mean that you would be forced to speedrun everything in the game as fast as possible. Gone would be the days of roleplaying actions like sitting at the campfire, visiting an inn and getting a drink, hunting some animals in the forest and getting a nice steak or decorating your base with the spoils of your adventure, as you have to constantly rush from quest to quest, trying to beat them as fast as possible, with little to no moments for careful exploration, or you would lose out on them.
A much better way to prevent the player from joining every faction with the same character would be to lock the player out of the enemy factions if they join an faction. For example, if the thiefs guild would have a problem with the fighters guild in universe, joining the thiefs guild would lock you out of the fighters guild and vice versa because they will see you as an enemy. That way you could limit players from joining every faction without having to apply a global time limit. That way, you could also design quests where the different factions interact with each other like for example having you destroy the thiefs guild if you join the fighters guild.