Depends on the event and what part of it your missing. First week of Gambit/EG are pretty low impact so if you miss those it because doesn't play to big a role in the rest of the event. Missing any part of shards is really hard though since its so short missing just 2-3 days can be killer. One of the shards event i used like 150 saved up puddings since I was gonna miss half the event and I was only like rank 450. Missing the second parts of Gambit/EG can really ruin your chance of getting the cards though. Especially EG since you have to be constantly checking for SEG if you want to reach 300 SEG kills. Gambit you can definitely do in one day if your able to play a lot, IE on the weekend, if you've managed to save up a lot of consumables or got lucky w/ Egacha.