24 Hour Time/Date Formatting Loophole

[WildBurrow]

I'm using a custom cell format in two cells (mm/dd/yy hh:mm). These cells are used to calculate elapsed time. Users are instructed to input 24-hour time (e.g. 1:00 PM is 13:00); however, they are managing to bypass my attempts to prevent the document from being saved with an invalid date format.

What I've discovered is this:

• If I put in 11/3/22 13:00, which is the desired format - things calculate properly
• If I put in 11/3/22 1:00 PM, the information converts to 11/3/22 13:00, and things calculate properly
• If I put in 11/3/22 1:00p (notice no space after the time), it won't calculate properly

I thought I had code that would catch any issues (below), but as stated above, it doesn't catch an 'a' or 'p' inserted next to the time.

'Error message if discovery date not valid
    If Not Application.Intersect(Target, Range("I3")) Is Nothing Then
        If (Not IsDate(Target.Value)) Then
            Application.EnableEvents = False
            Target.Value = "00/00/00 00:00"
            Target.Activate
            Application.EnableEvents = True
            MsgBox "Please enter valid date and time.", vbOKOnly + vbExclamation, "Date and Time Format:   mm/dd/yy hh:mm"
        End If
    End If

'Error message if reported date not valid
    If Not Application.Intersect(Target, Range("I4")) Is Nothing Then
        If (Not IsDate(Target.Value)) Then
            Application.EnableEvents = False
            Target.Value = "00/00/00 00:00"
            Target.Activate
            Application.EnableEvents = True
            MsgBox "Please enter valid date and time.", vbOKOnly + vbExclamation, "Date and Time Format:   mm/dd/yy hh:mm"
        End If
    End If

Is there any way to catch this issue in the Worksheet_Change(ByVal Target As Range) section?