*on textbox3.refresh
*This solution does not cover algebriche differences of time
this.value= LEFT(TTOC({^0001/1/1:}+ABS((CTOT(thisform.text1.value)-CTOT(thisform.text2.value))),2),5)

* on textbox6.refresh
like above

* on textbox12.refresh
* This solution does not cover when the sum overbound  24 hours : for this you have to choice what you want see
this.value=LEFT(ttoc({^0001/1/1:}+(CTOT(thisform.text3.value)-CTOT('0'))+(CTOT(thisform.text6.value)-CTOT('0')),2),5)