See https://experienceleaguecommunities.adobe.com/t5/adobe-livecycle-questions/need-a-date-time-field-to...
and generally in the initialization event of your time field (and your date field too) put some logic that prevents update if the field is filled. The initial state of a field NOT being prefilled by data is null.
Something like
if ($ == null) then
$.rawValue = Num2Time(Time(), "HH:MM:SS")
endif
Does the trick (Note: this is FormCalc and not Javascript as FomrCalc has better time/date support - but you could code in JS too, same princip)
