Authenticate once with a global admin account instead of authenticating each individual mailbox one-by-one.
Go to TOOLS > Mailboxes
Click on “Add mailboxes (multiple at once)”
On the next page, click on the “Bulk Link Mailboxes” button under the Microsoft 365 option.
You will be redirected to a Microsoft 365 login page. Sign in using a global admin account (or a Microsoft 365 user with a license and privileged administrator role) and accept the permissions.
You will be redirected back to timetoreply where you will see a list of all of your mailboxes. Tick the mailboxes you want to add to timetoreply and click “Save Mailboxes”.