They absolutely would have started on a Sunday. To the operators, it would have been just like any other work day - it's just that they're starting their new job locations on that day, or today, or tomorrow. It depends on the shifts that they've signed up for.
However, as APTA-2048 noted the start of the simulated service has been delayed as all of the operators get their refresher training. The simulated service will therefore start in the next couple of weeks once that has been done.
Delayed in the sense that you're not going to be seeing that many cars out on the line right now.
Dan