If the game is open, then close it.

Go into your device settings and find the time changer.

Then set the time to however long you want to have it for forward, don't set it past 11 months forward as it may break.

Then go into the game and claim your daily reward. If it is not the 15 min infinity pass then set the time 1 day forward and repeat until you get the 15 min.

Once you have your 15 minutes set the time back to the current time and you will have the infinity pass for however long you wanted it for! (in the screenshot I got it for 30 days)

You now have the infinity pass, you're welcome. :)