Hello @Jenny1788
In order to put in place a minimum stay length for the summer months and a shorter ones for the out of season period, you can opt in for the professional tools that are now open to us all and not just for those that have 6 listings or more. Only available from a computer!
You will get a lot of people looking for short stays if your calendar allows for this and then you are either stuck with accepting them and loosing out or refusing them. Yet if you refuse too many bookings this will affect your acceptance rating and your listing will be ranked poorly by the algorithm.
Here is a great guide on the subject:
https://community.withairbnb.com/t5/Community-Guides/Guide-How-to-Use-Pro-Tools-amp-Rule-Sets-to-Cre...
Use the search bar just above for other conversations on the topic and come back here if you have any questions!
All the best
Joëlle