I think the backpacks are already on the bus. I think teams without backpacks got there early, put their backpacks on the bus, then went sightseeing to wait out the departure time. Screencaps 18,19,20 look like a queue to get on the bus. Maybe one of those........."Get a departure time and take a charter bus" deals to another location. I see no indication of anything to do with that church or its museum. I think it is get a charter bus in the square in front of the church. Four teams are seen.....N/K, N/V, M/K, and B/C. Since the Peter and Paul Fortress is on its own little island, there may be driving restrictions there. So Production gets them charter buses to take them there? The teams without backpacks could just be sightseeing around the area waiting for the bus to leave at a certain time. If that is the case, then it appears that K/N helped Nick and Vicki find the location of the bus.
I think it is...detour first, then roadblock. The preview from last week sort of spells that out......with two racers fighting it out with the lawn game to escape elimination.
Looks like Jill/Thomas tried both sides of the detour.......plates or accordian. Stephanie is seen at the P and P fortress. No Gary or Mallory in any shots that I could see.
The 3 missing teams could be sitting on the bus for all we know.
Btw, St Petersburg is @ 60 degrees North Latitude. The sun will go down, but it will not get dark at that time of year. Pretty much the same as Anchorage, Ak at that time of year.