Immigrationboards.com

I'm in the process of applying for ILR for my wife and myself.
We first arrived in the UK on the 31st of May 2016, which means we can apply for ILR from the 3rd on April 2021 (5 years minus 28 days). Question I have, is this for the in person application? Can I submit my online form, book an appointment, pay the fees ahead of this? Or should I only submit the online application form after the 3rd of April?

The date of application is the date you submit and pay online. It has nothing to do with the date of your biomterics appointment with the thrid party agent ukcvas.