ringbark

If you stay at the same hotel for two consecutive nights, then it counts as ONE stay regardless of whether you check out and check in again or not. This is true whether your booking is one night and another night, or two nights.
I have done this for the same reason a fair few times and it has always been one stay. This is what the Ts & Cs say, unfortunately.

I've always thought it strange that Monday night in the hotel, Tuesday at home, Wednesday and Thursday in the hotel counts as two stays, whereas staying there for all four nights only counts as one stay, but that's what the rules say.
If you can be bothered and if there are enough properties in town, you can have two stays by staying in different properties on consecutive nights. I've found it not worth doing, but many others do it regularly.