When do master items get calculated?

[MartW]

Goodafternoon, 

a customer of mine created an app with lot's of master items:

- master visualizations

- master dimensions

- master measures

the app itself is very slow when opening, even if the same app is being opened for the second time.

my questions is, when do master items get calculated in general and is there a possibility that master items get pre-calculated when opening the app.