The renewal invoices are generated several days before the due time, and the exact day depends on the billing cycle. This means you cannot extend a VPS any earlier than that. However, you can add 'fund' to your account so it pays the invoice automatically when you have enough credit to cover the invoice when the invoice is being created.
Here is a table explaining the creation day of the renewal invoices:
Monthly services | 14 days before due date |
Quarterly services | 16 days before due date |
Semi-annually services | 18 days before due date |
Annual services | 25 days before due date |
Biennial services | 45 days before due date |
Check out the following link on how you can add funds to your account:
https://support.cloudzy.com/How-to-add-fund-into-my-account-and-how-to-check-my-available-balance.html