Hi,@Adele Vance
Thanks for posting your question in the Microsoft Q&A forum.
By default, working hours of resource mailboxes are 8:00 A.M. to 5:00 P.M. Monday through Friday.
You can refer to this command to check the working hours of this resource mailbox:
get-MailboxCalendarConfiguration -Identity <PrimartySMTPofRoomResource>
If the working hours for this mailbox is incorrect, you can run the following command to change the time:
Set-MailboxCalendarConfiguration -Identity <PrimartySMTPofRoomResource>
-WorkingHoursStartTime 09:00:00 -WorkingHoursEndTime 18:00:00
If my answer is helpful to you, please mark it as the answer so that other users can refer to it. Thank you for your support and understanding.