It is common to have an external nasal splint or cast and sometimes an internal nasal splint/packing after rhinoplasty. Typically an external splint or cast is removed 7-10 days after surgery. In some instances, depending what was performed during surgery, the surgeon may elect leave the external splint or cast on for longer. However, in my experience it is uncommon to leave it on past 14 days - it's usually falling off by this point anyways! You should ask your surgeon specifically when the plaster cast will be removed at your next appointment.
First thing is plaster casts, splints, stitches is very OLD school!! Splints are really bad coming out!! Sorry about that. Was you doc a facial plastic surgeon? Anyway, the cast should stay on for 5-7 days. Thats the standard!