Tax accounting date question

[Nestor Stura]

Hi all, my question is mainly for someone that could understand tax
accounting, because I do not.

This is my doubt:
In all my invoices I include the VAT and yhis goes to a Liabilities account
waiting for the payment every quarter. Each quarter should be paid on the
20th of the following month. e.g. Jan,Feb,Mar should be paid on Apr 20th.
When I pay, I discount from the bank account and add it to the liabilities
account, putting it to xero every three months.
I prepared a report to know how much to pay every Q amd my problem is that
if I add up inputs and outputs from that account, on 20 Apr appears an
input that corresponds to the previous Q payment distorting my accounting.
I thought about changing payment date to 30 Mar, but then I change my bank
account.

Do you know how to manage a posting that is done on a date but corresponds
to a different one?

Thanks in advance