@Euudoxia0 If you are just trying to unblock by clicking on the date and unblocking, that won't work.
If you are wanting to do this to accommodate a specific reservation request, go into your availabilty settings and uncheck the prep time setting until you get the booking squared away, then turn it back on.
If you use IB, you should also disable that until you turn the prep time back on, so no one can book dates where you still want the prep time.