Yes, the minimum storage period is 1 month. You will then have the option of paying for the next month or requesting a refund. If you need to store your personal items for a long period of time, there is no problem with the time you need to pay month by month.
If you need to remove the boxes or the stored equipment before 1 month no problem. Simply log in to your customer account and request a refund, but don't forget that the minimum period is 1 month so you will not be credited for the money paid for the remaining days after the return.