Whats is the best way to select several dates?


I don’t know whats is the best way to register several dates not continuous. I can not figure it out. I have a lot of people who replace to other people when they not go.
For instance:

Person X need to replace Person Y on 22 march, 25 march, 1 april, 3 april and 9 april.
How I can register this dates and then knows how many days are each month (2 days in march, 3 days in april)