Show a quiz at a random moment, between an interval

 Sorry, I shouldn't have said variable = certain number, I should have said if variable = 23.

Create a duplicate of that trigger for when timeline reaches 10 minutes if variable = 10, one for 11 minutes if variable = 11, one for 12 minutes if variable = 12, one for 13 minutes if variable = 13, you get the idea.

I guess if you have to, you can create 60 of them, one for each minute, set variable 1 to a random number between 1 and 15, variable 2 between 16 and 30, and change the conditions accordingly. That would give you four interruptions unpredictably between set intervals, which is what the original asked for.

Or set all variables to completely random numbers, and have the condition check them all.