Access Subform Time textbox - send value to Main Form

I have a Form with a SubForm.  

The Subform has a Time Selector.  It is comprised of 4 unbound textboxes.  the first 3 textboxes the user clicks a control button that is is functioning as and up or a down to increment by 1

The 4th text box also unbound is where I take the input by the user and combine it to get the time value

That textbox is [tbTime] On subform [frm_DataDetail]

The code which on the textbox of the Subform works is:

=IIf(nz([tbHr],0)=0,"",IIf(nz([tbMin],0)=0,"",IIf(nz([tbAMPM],"")="","",(TimeSerial(IIf([tbAMPM]="AM",[tbHr],[tbHr]+12),[tbMin],0)))))

Now then I want to bring that time from the Subform over to the Main Form into another unbound textbox.

That Main Form's textbox is named [tbTimeInput]

I have keyed the following code which is not working.
=[frm_DataDetail].[Form]![tbTime]

All I Get is the #Name?

I have done the same Control Source formula to get data from a Subform to the Main Form for other numbers but since this is "Time" is there something else I must add?????

That textbox is formatted "Long Time"

That SubForm 4th Textbox is in the Footer if that makes any difference.