Every 30 seconds is something that has to do with trial and error. I wouldn't use 30 on the dot, though, because then it would be predictable.
As for the 16 times thing, each individual time should have a different intangible invisible FOF that executes, moves out of the way, and brings the next one in.
What? You asked for it. Don't tell me you seriously expected the map to play for 8 minutes on the dot.