This is a small airline with 5 puddle jumpers, not Easyjet or BA. Resources are likely to be very limited.
The person(s) doing the switchover likely works on a UK bodyclock. If the changeover takes maybe an hour or two, then best to let them do it when everyone is reasonably alert, instead of at 3 am, and other people are available to confirm all is ok or make a decision to roll back the changes
That said, 8 am on Sunday morning is maybe a better idea...