Close AP Period before GL

I unfortunately don't have access to a test system at the moment to try this myself but someone has told my boss that AP cannot be closed say on the 28th of the month.  The only issue I can see is that if they key an invoice and the GL date defaults to sys_date it will give them an error that the gl date is not in an open period but they could then change it to the first day of the open AP period.  Does anyone know of any other issue it might cause?

So we would close AP on March 28.