Depends on your problem domain. You can be Twitter/Discord sized and get away with 64 bits. When you start dedicating parts of your UUID to a timestamp the possibility of collisions does go way up since now a significant chunk of the UUID will be the same for everyone. But when you deploy this variant you aren't trying to make globally unique ids anymore, you're trying to make application unique ids. You are sill very unlikely to not also have a globally unique id because 128 bits gives a lot of room to play around.