house sitting start time?

I have it listed clearly in my profile that when booked for housesitting, it starts the evening of that booked day, and ends on morning of last day. Otherwise, what would happen is someone might book for one night, but expect you to start at 7am and end at 10pm following day, which is essentially two days while only paying for one.

I got a booking request and directly messaged this to a new owner when inquired about booking - he confirmed this would not be an issue. Booking was confirmed for housesitting about two weeks ago for this weekend (3 dogs, 1 cat). I agreed to start at 6pm, which is their usual dinner time. Now, 2 days before the start date, I get a message saying he is "asking that I start the morning of" because they are leaving earlier than originally planned and plan to crate their animals the evening prior. He never even asked me if I am available that morning. This is exactly why I clearly state start and end times. Boundaries can get so murky and while I want to be reasonable, expectations need to be clear. I am thinking of telling him that he will have to either modify the booking to start the evening prior, or pay for extra service of a drop in visit that morning. Anyone else have anything similar happen, and how did you handle it?