Okay, here is what you do:
Create a form and hide it.
Set the form's Visible property to False so that you can't see it when it opens.
Open the form when the application is opened.
On the form's Timer Event, you want to place code that goes out and checks the current time, like every 30 mins or so.
If the time is >= your update time (AND <= about 45 mins after your update time), then run your code that goes out and does your update.
The code might look like this:
Me.TimerInterval = '30 seconds = 30000, so do the math
Dim curTime As String
Dim upTime As String
curTime = cDate(Time())
upTime = #13:15:00:00#
If curTime >= upTime Then
'call your update code
Someone help with the syntax. I don't have time today to test this.
Anyway, conceptually, this will do it.