One minute is more than adequate. If more time were required, the warnings in the manual would say so.
The "backup supply" is in the airbag control module. It only needs to maintain power for less than 200 msec in the event of a crash (and loss of primary supply) in order to activate the system.
It's a small capacity. There's no need to be timid around it, but it does need to be respected.
Steve
