Personally I hardly ever knock in bats for much longer than an hour or two just on the edge and toe, personally find just tapping an old ball on the bat for 5-10 mins per day works fine. I keep most of my kit on an abounded floor at work and put a ball in an old sock to do edges and toe, that's how I was first shown how to prepare a bat and have always done since. Does help I don't try and smash bowling ever really though.
Other benefit of facing bowling machine is you can start at easy pace and get used to how the bat feels and get used to it.
Some must spend there whole life knocking in bats with there collections chad and Simon may must never stop lol