@LindaNC great question
It all depends on your location
If your location has a popular annual event / festival that it’s famous for - sitters would love to stay during that time to enjoy the event . https://forum.trustedhousesitters.com/t/cherry-blossom-season-in-south-korea
-If you are in an area that gets cold over winter many sitters would prefer not to sit at that time but would enjoy being there when it’s warmer . If you are in a location that gets exceedingly hot in the summer ( and most locals are leaving for cooler areas ) then most sitters also would not want to stay at that time .
If your sit is family friendly - School holidays are popular times for families that sit .
However there is an over saturation of sits at Christmas holiday time which means not all listings for these dates get sitters.
If your previous sitters had a reason to be in the area ( e.g visiting family ) you might reach out to them to ask if they want to stay again and book your holiday around their dates .