I'm answering with information about how HST works... not about how Sage works.

Usually, the time lines for HST reporting are:

1.  Revenue - report based on the earlier of the INVOICE DATE and the DATE YOU RECEIVED MONEY.  (Usually, you won't get $ until after you send the invoice... but remember this rule if you ever receive a large deposit or prepayment on a job.)

2.  Expenses - claim the Input Tax Credit within 4 years of the date of the expense invoice.  Make sure that the expense invoice has the required information on it.  (For a chart, see Input tax credits - Canada.ca)

Thank you for the reply C White.  We have not received any payment for the invoice I am speaking of as we have not sent it and we have not received any type of retainer for the project. 

Then it certainly makes sense to change the date on the invoice to whatever date it will actually be given to your client.  No need to give the government their money early!