Right now many players can’t play the Mobile Madness blitz events because of a time zone issue in the game.
Quick solution until the fix is deployed: Close the game, change your time zone to Sydney, +10 GMT on your smartphone/tablet and start the game again.
The fix should be deployed today.
Set time, date & time zone for Android devices: https://support.google.com/android/answer/2841106?hl=en
Set time, date & time zone for Apple devices: https://support.apple.com/en-us/HT206986