Return Value In Same Row

I have two criteria that need to be met when running a macro to record a timestamp. First - the timestamp needs to be recorded in the first blank cell in the correct column, based on a selection made in a userform. Second - the next timestamp taken needs to be recorded in the same row as the previous timestamp. The times are being recorded in columns D, F, H, and J. So as an example.....

I record the time in column D, but I skip column F and record the next time in column H. That's fine - the timestamps are in the same row (say row 8). Now I record the time again in column D, one row down (row 9).. But this time I don't skip column F.. the time doesn't get recorded in row 9; it records in row 8.

Sub MacroD()
Dim LR As Long
LR = Range("D" & Rows.Count).End(xlUp).Row + 1
ActiveSheet.Unprotect
Range("D18:D" & LR).Value = Now
UserForm1.ListBox1.Text = "Time"
UserForm1.ListBox1.SetFocus
' UserForm1.Show
End Sub

Sub MacroF()
Dim LR As Long
LR = Range("F" & Rows.Count).End(xlUp).Row + 1
ActiveSheet.Unprotect
Range("F18:F" & LR).Value = Now
UserForm1.ListBox1.Text = "Time"
UserForm1.ListBox1.SetFocus
' UserForm1.Show
End Sub