I'm strongly considering to implement day/night change. For example duration of the day will be 20 minutes and duration for the night will be 10 minutes. During night visibility is reduced and units don't have circle vision but triangle vision (pointing according their orientation). I'm thinking about villagers returning every evening to their homes and going back to work in the morning. I'm thinking about sending spies in the night to some cities and making unattended espionage or making a night ambush and when city wakes up in the morning there is enemy all around (side note: cannot happen to city that never sleeps).
The drawback is, you can't do much during the night (10 minutes). Maybe do some tactical decisions, calculating your daily profit, setting new prices in shops or designing your city layout.