[quote name='FriskyTanuki']Nobody ever spawned for me without Bob telling me about them himself, so it was required for me to get all of the survivors. I'd go to the three areas where survivors spawn first and nobody would be there without Bob's wave to signal his approval of unlocking a new survivor. I even got so pissed by this on one playthrough that I shot him in the face until he turned on me and locked myself in his store for the rest of the game, which he'd try to shoot me through the door as zombies slowly killed him.
Even with those issues, he's still a lot better than Otis.[/QUOTE]
Bob won't start telling you someone is around until you exit and re-enter the map, from my experience.
Example: It was after 1pm, so I was looking for Tia and Nikki so I could get them and Sharon, but they never appeared... Bob wasn't yelling and screaming for me going to him either. Then I went in the safehouse for something. When I exited, Bob was hooting and hollerin' and since it was after 3, both Tia/Nikki and the handlebar guys spawned. I've tested this on my multiple playthroughs and it works for me.
I had all bike parts minus the handlebars, all doors opened, pawnshop open, and the couple in the bar saved before 1pm and Nikki/Tia weren't there yet. I waited until Chuck's watch hit 1pm exactly and left the safehouse again -- sure enough, bob was screaming to me to come talk to him.