They pulled this crap on me - one time.
A few years ago, I took a night-stocker's job there for some beer money after retirement. Got $1 hour extra for the graveyard shift, making it about $11. Worked three hours OT one week and on the last day before the pay period was over, the supervisor had an Oh Crap moment and told me I had to go home three hours early. I raised Hell, saying I came there to make the bucks, not go home at 3:30 a.m. instead of 6:30.
That went on for 15 minutes and the guy ended up saying no one have ever talked that way before, BUT, I had to go home. From then on, I always made sure I was out the door at normal quitting time.
On the flip side - we were in our local store and noticed more help on the floor as well as "The Return of the Greeters". (One flat screen TV walking out the door cancelled any "savings" they made by not having someone there.) Wife talked to one of the women, who said they were putting more people on the registers.
The two Walmart stores in my town are now closed at night. I’m sure to save payroll costs.