Ah! With what I know that might be a problem without changing the master schedule in the admin section.
One way to perhaps get around that is - create a provider called Room2 as first name, have that provider with more extended hours, give full previliges to that Room2 (first name) provider. On that particular day, book the patients under Room2 with different set of hours. During regular day, tell your staff not to book in extended hours. Of course you could still use that Room2 for your own patients if you want to double book for that time slot.
Hope this helps.
Regards-
