28 days funding for tier 4 visa

Hi All,
I need some help, please.
If a student got CAS from the university, but he/she not yet fully filled the 28days funding in the bank account. Does he/she have to wait to complete 28days to book a visa appointment? OR can drop visa application and select slot which comes after 28days of funding?

Thank you.

Please, anyone to help on the above query...

You need to have the 28 days of funding in place, and the evidence of it, on the day you make the online application. The application form asks you to confirm it, then upload the documents.