I would presume that as a student allowed to use the school harp you must be taking lessons from a teacher there. Have you just asked about whether there’s a way to increase time or, if the harp is just present in the room but not used, to move it into another room when other instruments are being taught there?
In any case, if you have a teacher, he or she can answer your question about the lever harp far better than we can, since that’s the person who knows what repertoire you’re playing and at what level.