Someone posted an opinion that the birds emerge at 5:30 am. I don't know
how consistent they are, but on Sept 3, 2005 I took video of the emerging
swifts. Although I arrived before sunrise, the first birds emerged at 8:07.
Before that, a few swifts were circling and entering the chimney. By 8:30,
the show was pretty much over. A few swifts were still in vicinity and from
time to time a few would enter. So, you can probably roll over and get
another hour's sleep before going to see the swifts emerge.

Al Wagar
Shoreline