20-60 second delays are quite long, so forget about using "Wait" action.
Add Timer behavior to one of your objects (background sprite for example) and a variable "callCounter".
Then you can do something like this:
On start of layout
[ul]
[li]> Sprite start Timer "CallFunction" for random(20, 60)[/li]
[/ul]
Sprite On Timer "CallFunction"
callCounter<3
[ul]
[li]> Add 1 to callCounter[/li]
[li]> Sprite start Timer "CallFunction" for random(20, 60)[/li]
[li]> Function call ...[/li]
[/ul]