Need Help! prevent users from requesting a duration that exceeds their remaining time quota

Hi everyone, I’m building an attendance utility in App Inventor. Each user has an annual time quota of 6 hours, and they can “use” portions of it (example: leaving 4 hours early deducts 4 hours from the quota) and if excess the quota like only about a minutes, the system won't accept automatically.

The quota is stored in a google sheets as a text string, for example "6:00:00" or "1:00:00". but i have no idea how to solved it.

Please help