Yes there is a delay. The fan runs to purge gases from the fire box AND to make sure there is circulation before igniting. The air circulation monitoring is via a sail switch. If the sail switch does not close no ignition will take place.
If your battery is low there will not be enough energy to spin the fan fast enough to make the sail switch contact. Also sail switch can get some scmuts on them which will prevent closure of the switch or the sail switch could be bad
Traveling with my best friend, my wife in a 1990 Southwind