I think it depends on the regulations of my own school to postpone the defense ~LL it is best to ask the academic affairs office, after all, the system of each school is different.

For example, in our school, the deadline for formal defense is 15. If a student postpones his defense, that is to say, he will get his diploma 3-6 months later than the student who defended at our official time.

LL, you'd better ask your school how to postpone the defense.