Tooth #13 pulled & would now need bone build up for later implant. How long til I can wear a temporary tooth. Is this even possible? Flexy denture?

Up to surgeon. You do not want to disturb the surgical site. Three to six weeks may be needed for adequate healing. The more time the better.
Timing. Your surgeon and restorative dentist (unless one in the same) can discuss timing of bone grafting and placement of temporary prosthesis until healing is adequate for an implant and restoration. We often make an immediate replacement which would have to be modified one or more times for grafting and implant fixture surgery.