Timing Belt (TB) is located inside the black plastic cover and the Crank Pulley (CP) is outside of this cover.

So, you can replace the CP any time you want without disturbing the TB.
No need to be at the same time.
TB service will require lots of preparation/procedures even before being able to access the TB itself so replacing only the CP is much easier.

You'll need to remove the CP again at the time of TB service but I would be happy to do so knowing that the CP Bolt would come off with ease as it was cleaned/greased properly and more importantly, I don't need to worry about the CP issue.

Kaz