There is also the "open chest in the shop five times" quest after "level up event epic girl to Level 5." Unless you have gems to spend, this will take 20h to finish, so you have to grind pretty hard to reach this event a day before the event closes. With the "beat event monsters 25 times, open chest in the shop 3 times, then 4 times, and get so many event girls which requires waiting for event monsters to respawn, there are a lot of resisters to pass through before we even reach the three quests you listed. In fact, one of the only reasons I was able to go beyond the quest to get the legendary girl is that I have been temporarily out of work since Wednesday (due to covid) and today is Memorial Day. Normally it is quite a difficult grind to get the legendary girl when I have work (although it is still doable).
How do you make the open chests and beat monsters quests go by faster?