Okay, thanks for this guidance! See my responses below:
1. DT>0, RT>0, OT>0
Set Me.txtbox_TotalTime = "RT: " & txtbox_RT & "OT: " & txtbox_RT & "DT: " & txtbox_DT
2. DT>0, RT>0, OT NOT >0
Set Me.txtbox_TotalTime = "RT: " & txtbox_RT & "DT: " & txtbox_DT
3. DT>0, RT NOT >0, OT...