Are you taking about setting up a bank account? If so you can’t do so online. You have to do in person. Almost impossible task these days without a long term visa (and many reports of issues even with one).
It’s not a time of day thing. It’s up to 3 days prior. If you’re say arriving on a Sunday then the stroke after midnight on the Thursday (so Friday morning) you can apply regardless of what actual time you will arrive on Sunday.
You need 800k in the bank for 2 months prior to application. The fact you already had an extension means you need to have followed the rules for that one which would have been to keep the 800k for 3 months after your extension and not go below 400k for the remainder of the year - and then back up to 800k two months prior to application.