I want to send the recurring invoice email reminders on 25th every month. How can I do this?

In order to send out the emails on a specific day in the month for recurring invoice subscriptions, you must have a recurring invoices subscription rule with a monthly interval type. When the monthly interval type is selected, you will see an option to select a day in the month when you want to send out the invoices.

In case you have a weekly interval selected, then you will be able to select the day of the week when the invoices get sent out.

Here is an example:
Let's say that you have a monthly subscription and you configured the app to send the emails out on 25th day of the month. Your customer creates a subscription on 2020-11-26.
The subscription email would normally be scheduled to be sent on 2020-12-26. However, because you set the app to send out emails on 25th day, the system will send all emails which would normally be sent in the period from 2020-12-25 to 2020-01-24 on 2020-12-25. Your customer will receive the email on 2020-12-25.
This functionality always sends out the emails from the period after the desired day, so you have enough time to package and send out the orders.