A product is never finished. You'll just continue to develop it as long as you have customers.
This is due to a number of factors:
- new tech emerged
- new requirements came from existing customer
- new requirements came from potential new customers
- a new competitor entered the market
- you are innovating
- user expectations and behaviours changed
- industry standards and best practices evolved
- regulation and compliance changed
- you need to integrate with new platforms and services
- your business goals or strategies changed
- you've accumulated tech debt
It's unheard of to not see any of these factors so that you'll have time to slow down, catch your breath and fix accessibility. Don't plan on it.
It's rare to do things right from the first try also. Don't plan on that either.
Instead, plan on things constantly changing and you having to fix things as you develop. Plan on integrating accessibility throughout your SDLC.
And then execute on that plan.