AFAIK your rest time doesn't start until you are resting.
I always took it from when we hit the hotel or got home, etc.
That would be the ideal
18 but companies I have worked for say you are off duty, (and therefore into your rest period), 30 minutes after chocks in
so in places like Bombay, (Mumbai) and Bangkok where the bus journey can take one to one and a half hours there wasn't a whole lot left if you were on minimum rest.