Access VBA: Form timer not showing MsgBox at the intended time - ms-access

Question

I am trying to get the DB to close after 2 minutes have passed by (for testing purposes I am just making a MsgBox appear after the 2 minutes). To do this, I have a main form called DTForm and a hidden form called Timer. Both forms open on opening the DB but Timer opens in hidden mode.
AutoExec Macro:
1. Open DTForm (the main form)
2. Open Timer (the hidden form)
Module 1:
Option Compare Database
Option Explicit
Public timer_start As Date
Public timer_end As Date
Public timer_diff As Integer
DTForm (users will only see this form)
Option Compare Database
Option Explicit
Public Sub Form_MouseMove(Button As Integer, Shift As Integer, X As Single, Y As Single)
timer_start = Time
timer_end = DateAdd("n", 2, timer_start)
End Sub
Timer (the hidden form):
Option Compare Database
Option Explicit
Public Sub Form_Open(Cancel As Integer)
timer_start = Time
timer_end = DateAdd("n", 2, Time)
End Sub
Public Sub Form_Load()
timer_start = Time
timer_end = DateAdd("n", 2, Time)
End Sub
Public Sub Form_Timer()
timer_diff = DateDiff("n", timer_end, Time)
If timer_diff >= 0 Then
'Application.Quit
MsgBox "timer reached 0"
timer_start = Time
timer_end = DateAdd("n", 2, Time)
End If
End Sub
Update - the problem: So now the problem is the mouse. It looks like just moving the mouse around the form does nothing. However, moving the mouse from the navigation pane to the form and back (in and out) does trigger the mouse movement. This seems really counter-intuitive - why not just consider all mouse movements?
Notes: Added Option Explicit to the tops of both forms and fixed some missing variable declarations.

Answer 1

This seems to be a variable scope issue to me. By default your variables are local.
Unless timer_end is declared as a global or public variable, it is out of scope as soon as you leave the sub where it is defined. So the timer_end in Form_timer is a totally different variable than the one in your MouseMove event (even though they have the same name).
This is one reason why many people put "option explicit" at the beginning of their code as it forces you to declare your variables.
You could also pursue a design strategy where you pass the variable as a parameter instead of making it global or public

Answer 2

If you want to go through with it, the Form_MouseMove event must be in every form, because only the active form receives the MouseMove event.
Note: you actually don't need the timer_start variable at all. You can remove it and keep only:
Public Sub Form_MouseMove(Button As Integer, Shift As Integer, X As Single, Y As Single)
timer_end = DateAdd("n", 2, Time)
End Sub
Or somewhat cleaner:
Public Sub Form_MouseMove(Button As Integer, Shift As Integer, X As Single, Y As Single)
Call UpdateTimer()
End Sub
and in your Module1:
Public Sub UpdateTimer()
timer_end = DateAdd("n", 2, Time)
End Sub
in case you decide to change the time interval...
Note:
timer_diff should be a local variable in Timer.Form_Timer(), since it's only used there.

Answer 3

DateDiff("s", timer_end, Time) will return a negative value until the 10 seconds of inactivity, then the condition must be changed to >= and the time interval to 1000 (1 second) 1 millisecond is too fast.
Also to make sure the variables are ok add option explicit clause
Option Compare Database
Option Explicit
Dim timer_start as Variant
Dim timer_end as Variant
Public Sub Form_Open(Cancel As Integer)
timer_start = Time
End Sub
Public Sub Form_MouseMove(Button As Integer, Shift As Integer, X As Single, Y As Single)
timer_start = Time
timer_end = DateAdd("s", 10, timer_start)
Me.Label6.Caption = timer_start
Me.Label8.Caption = timer_end
End Sub
Public Sub Form_Timer()
If DateDiff("s", timer_end, Time) >= 0 Then
MsgBox "timer reached 0"
End If
End Sub