Only chance to book super priority when submitting ILR application?

Is your only option for booking super priority when you submit your ILR application? From reading other topics, only so many super priority bookings are made available every day, so are you out of luck if you submit your application and there are no spaces or can you try again later (after submitting)? I couldn't find a definitive answer to this elsewhere and don't want to submit an application without knowing in advance what to expect.

Is your only option for booking super priority when you submit your ILR application? From reading other topics, only so many super priority bookings are made available every day, so are you out of luck if you submit your application and there are no spaces or can you try again later (after submitting)? I couldn't find a definitive answer to this elsewhere and don't want to submit an application without knowing in advance what to expect.

It is. If you submit the application without securing a priority slot, you do not then get the opportunity to add it later.

The slots become available at 12 midnight or 1am depending on whether we're in British summer time or not.