Sure! But that’s 100% up to you.
If a volunteer wants to stay for a shorter period of time than what you ask in the platform, it’s up to you to decide whether to accept or not. Keep in mind that volunteers might have their own availability to travel (maybe they have less than 2 weeks off from work/school), but you should decide what’s best for your place and how much help you need.
Most hosts set their minimum time to stay for two weeks. That is usually enough for the volunteers to learn their to-dos and enjoy their stay! If you need people for more time than that, you can choose a longer minimum time to stay. Go to “Volunteer Positions” → “Edit” → “Stay for”.
Remember to change the dates on the pre-approval if you have agreed to host the volunteer for a shorter time.