It depends on which Application Table you are using to calculate your funding amount.
If you are using Application Table 1, you don't need the exact date. Try to be as accurate as possible with your entry.
If you are using Application Tables 2 or 3, you will need to know how many months you were making sales (either in 2019 or 2020) so that you can correctly calculate your funding amount. It is important that you are accurate with the date.