depends on what bus.
here are the statistics.
LO3x - 16seconds
VO3x - 18s
VSO - 15s
Trident - 13s
B9 CDGE - 16s
B9 Wright (moving) - 16s
B9 Wright (at traffic light stop) - 15s
VO2x - won't reach, escape via windows.
hope this helps!
adding on a varience of about 6s (excluding VO2x) as well as
factors such as aircon speed, temperature and structure of aircon
duct, and the amount of people standing on the lower
deck.