Bees in bird box; how to know when they've gone?

Good morning all,

We have had the fortune to have bees in one of our bird boxes this year, signified by dizzy drones circling the entrance of the box.

Over the last week or so the activity has decreased and we have barely seen any so we're wondering how to know when the bees have flown the coop! 

I do not want to disturb them if the they are there but would rather like to put back relocated furniture and trim back the rose in the immediate vicinity and so any help would be greatly appreciated.

Thanks very much 

Will