Signing up to OVO - when do I find out the Direct Debit payment date?

I'm looking to Switch to OVO but the application doesn't mention when the first payment will be taken. Can I specify when I want to switch ie the 1st of the month?

Hope you found a tariff that you like, @Kinhell

Your first Direct Debit payment will tend to be soon after your supply start date. This will be confirmed in your Welcome email, sent 3-4 days after you click on that signup button!

You do have the chance to change this Direct Debit date though: https://forum.ovoenergy.com/billing-payments-35/changing-direct-debit-date-617

Tim