Date we count the interest on delayed deposit of st?

Hello experts,

Our client is under mandatory e-payment of service tax as the payment is above Rs. 10 Lakh.

Now, from which date we shall count the delayed interest, is it 6th of the month or 7th of the month in which tax is due.

In my opinion we shall count delayed interest from 7th of the particular month in which tax is due as we require to pay e-payment but unable to find any specific circular or section clearing this point.

Please, confirm this point and it would be best if we have some reference.

Thank you with expectition.

Regards,
Abhimanyu