With a Premium account, there is no limit on the number of meetings you may create.
In the free version of Pinstriped, the number of active meetings you can have at any given time is limited to 3. Any meeting created or imported into Pinstriped and showing in the meeting list is an active meeting.
Once the limit is reached, you must delete an old one to make space for another. Be aware that once you delete a meeting it is deleted completely and forever and links in emails sent to participants, stop working.