Just to add on my duels note below, the conditions to have two wars in one day is very rare and hard to achieve.
Updated Jan 20, 2020 Wars last 30 min prep + 2 hours. War cooldown is 20 hours.
30 min + 2 + 20 = 22.5 hours, with only 1.5 hours left in the day, it’s not possible to have 2 wars in one day under normal circumstances.
In order to have 2 wars in one day, you have to force instant defeat (enemy has no ACs left standing):
30 min prep + up to 30 min war + 30 min instant defeat timer
30 min + 30 min + 30 min + 20 hour cooldown = 21.5 hours would give you enough time to another 2.5 hour war.
However, your opponent will need to have enough time for a war themselves, so often times, you will war the same alliance twice or an alliance that didn’t war yet nor do they have a truce timer of +16.