\HKCU\ControlPanel\Notifications\{A877D660-239C-47a7-9304-0D347F580408}
Options
Value data: 1073741845
Decimal
Changing this registry setting enables the Repeat option as well as "Flash Light for 15 minutes".
You can make changes to any of the options, as needed and the Repeat should stay enabled.
changed Duration from 15 to 230.