The thing about this is if a lot of people decide to wait longer than they have been told it screws up what is a very complicated logistics exercise managing the vaccine stocks around the country. They could end up with expired doses that get thrown out and wasted, and/or suffer shortages when a bunch of people turn up later than expected. I recommend doing as you're asked tbh.
Edit: I do understand where you're coming from on the efficacy front though.
Edit: I do understand where you're coming from on the efficacy front though.