Greeting!

we are a small internet service provider are giving services to our customers.

1- all Service payment from customers are advance and customers should pay their invoice before start new month.

2- all customers billing date is 20th every month . it means customers should pay us maximum on 19th every month to renew their service for next month.

Question:

My question is that How I can setup my Zoho that make invoice about 4-5 days before 20th ? because I should send invoice of service for customer and they arrange their payment for renew their service.

Thanks