If Im not mistaken, you want to add first two values of your text boxes..

You can do this by getting the value for every single textbox..

Store CTOT(thisform.text1.value)+{^2000/01/01:},2) to nTIME1
Store CTOT(thisform.text2.value)+{^2000/01/01:},2) to ntime2

You have to extract the time in numeric format using SUBSTR() then add them..
then multiply to your rates...