When u get there, you've got to take a ticket from the "number" machine ...... a bit like the meat counter at Sainsbury's !
You should be able to work out from that when you'll be called.
Then you can both go & get breakfast.
BTW ... for passport renewal, you need to queue up twice.... once downstairs to submit the form & pay.
Then upstairs to do the biometrics.
They also close at 1pm for lunch (on the dot !), so if u haven't got it all done by then....... then you've gotta return at 2.00pm.
Enjoy !