NRTFT, but...
Cleaner here. I don't do dishes. Simply because you do a couple one week because it wont take long, but next week there are more. The week after, even more. Before you know it an entire weeks worth of dishes have been allowed to grow to the size of Mount Kilimanjaro, growing bacteria and mould and hard as cement. It's not on. It's vile on a health & hygiene level. It's just downright disrespectful on a personal level. And it affects the length of time the clean takes, so if I'm spending an hour scraping, rinsing, scrubbing, degreasing, drying and putting away, it's going to eat into the time. Other tasks don't get done because I need to leave at the end of the slot time to get to my next job. And then complaints start. And then arguing ensues when I have to point out I had to spend so much time on the avalanche of mould-ridden dishes.
So I set my boundaries from the off - I don't do dishes. End of, no negotiating.
However, I would never leave early. If you're paying for 2hrs of my time, 2hrs of cleaning is what you get. (Just not dishes!)
Ps. 2 cleaners for 1 hour = 2 hours. Not, as you put it "I pay for 2 hrs, but have 2 cleaners, so only 1 hour". You have 2 MAN hours. Each cleaner needs to earn the hourly rate for the hour of work they've EACH completed.
But do chase up with management as to why they left 30mins early (unless they gave you a job rate for an agreed set list of tasks, rather than an hourly rate for a set time - then that's different. If they completed all the agreed tasks for the agreed job rate, then you have no right to complain)