It sounds like you don’t have a reservation booked to build one? Are you hoping your guide can get you in? Maybe see if they can book one for you for when the tour ends so you aren’t wasting touring time building the light saber? But I don’t know if they will be able to book it if there isn’t availability. If you start at 9, and the max amount of time the tour can be is 10 hours, you will be done by 7, so I would see if they could make an appointment for you when it’s over.
We took a relaxed pace on our tour, but even so, I don’t think I would have done an extra like that during that time. At approx. $600/hour, that seems like a lot of money to not even get any benefit from the guide.