A very sensible timed event in BG3 would be the raid on the grove. If you tell Minthara where it is and she leaves to go raid it, then long resting afterward should result in you missing the raid entirely. Or at very least the raid is already in progress when you arrive, with Minthara+goblins just having broken through the main gate.

This retains player agency by letting the player determine when/if they tell Minthara of the grove location. There is little risk of missing out on other things because the ~rest of the world remains the same whether you go to the grove immediately or long rest. But it also adds to the immersion of the world; things can and do continue without you and you should keep this in mind for future events.

The only downside is that players might be forced to go into a fight without full resources, which is fine. Aside from resource management being a generally good thing, BG3 offers more than enough consumables to make up for missing abilities/spell slots.