Do you mean learn one that's dependent on learning a new sleight, or not?
Learn it so you could get through it for your magician buddies, or learn it with a newly written script, with the blocking, and pocket or prop management to a level where I would do it at a paid gig?
An hour or two for the former, years for the latter. Clients deserve to see material that has been polished to a shine, not something you picked up last night. We owe it to each other to give clients and audiences the best experience of magic we can, because if you gave them a great show, polished and professional, they're more receptive to seeing me.