Sundays are notorious fur folks "calling in" and taking the day off. I offered to come in 2 hours early to ensure coverage. They said "Oh, come in and be there in case somebody doesn't come". I say "What if they do?".
"Start at your scheduled time", they said.
So come, just sit there, unpaid, on an early Sunday morning?
I stay home fur two hours.

Seriously.

They should have more appreciation for your work ethic.