see boot(8). you need to wait 15 seconds for the default to be picked up:
"Method and address are prompted for first. The prompt lists all valid
methods, with the default in brackets, for example:
root is from (tcp, local!#S/sdC0/fs)[tcp]:A newline picks the default. Other possible responses are method or method!address. To aid in automatic reboot, the default is automatically taken on CPU servers if nothing is typed within 15 seconds."
