Revenue Protection Officers can be on ANY train service, from the earliest to the latest services.
It’s a bit pointless if all the ticket dodgers have to do is travel before the RPOs start work for the day, or after they’ve all packed up and gone home.
If you love the job, you’ll soon get used to working unsocial hours and even to enjoy it. I work in UK public transportation and although I don’t love 4:30am starts, I do love finishing work at 12:30pm and having the rest of the day to myself. The roads are empty that early as well so my usual 90-120minute drive to work stuck in heavy traffic only takes about 45 minutes. Likewise, when I start at 6:30pm for a 2:30am finish I get the whole day to myself and a really easy and quick drive home.
Apart from the start times, you need to consider that there will be times you must travel further to work depending upon which station or depot you’re starting from that day, particularly when there are targeted exercises against fare dodgers.