Let's say you have an open manual invoice and you record an ACH payment on April 1st. However, you choose a date in the past for it to be applied to, such as March 28th. You post the payment and check the Billings dashboard (Daily view) the day after and find that the payment was not posted for March 28th.
The Billings dashboard will use the date that the payment was manually recorded, not the date that you selected the payment be applied to. So, in this case, the payment would be counted toward April 1st, not March 28th since that is the date that it was recorded in the Recurly UI.