You can do this in your Personal Account when setting up your Listing in the Property section using the Set parameters button (step 6). 

The range of minimal nights is a parameter that determines the lesser number of nights at your Property that can be booked by a Guest depending on your calendar’s occupancy.

Diwerent’s algorithm will aim to sell as many nights at your Property as possible. The greater number of the range will be used by default if the calendar has many adjacent open dates. When the number of available adjacent nights becomes limited, our system will allow your Guests to book a lesser number of nights within the range.

For example, if you set a range of 5-7 nights available for booking and you calendar has mane available adjacent dates, your Guests will only be able to book 7 nights minimum. If there are only 6 adjacent nights available, the system will let the Guests book 6 nights, but not 5. Where only 5 nights are available, 5 nights can be booked. And if the number of available nights is less than 5, no one will be able to book them.

If you do no want to set a range, you can just set a flat number, for example, 3-3. In this case your Guests will always be able to book the minimum of 3 nights.