Can someone reveal whether you can visit Birsay off hours? On the days we plan to be there, the low tide is 7pm-ish. I used Street View in Google Maps and couldn't see any sign of a fence or gate. I've also read that many people skip the entry fee, so maybe there's just a deposit box? Paying is not the issue - it's whether the causeway is accessible when the site is "closed".
I think I found the answer after making a more specific search. It is accessible 7/24 as tide permits.
Do pay attention to the tide times - you don't want to be cut off there!
And don’t think you can fool with the incoming tide—it will overflow the causeway and leave you stranded very quickly. I believe the park ranger turns on a siren/alarm before they return to the mainland to let anyone left on the island know they only have a few minutes.
I'm a sailor in the Pacific Northwest, so I know all about tides, and wouldn't cross if there wasn't oodles of time.
I kept returning to this thread, thinking the OP wanted advice about whether to visit "Brough or Birsay" -- then I finally looked it up and learned that the name of the place is Brough of Birsay. The OP may want to edit the title of the tread, if that's possible.