Time format with seconds (as in “duration”)

Hi, I’m finding it difficult to find a Time format that simply reads hh:mm:ss (Hours, Minutes & Seconds). the point is to choose a duration. I’ve tried various options from Flatpickr where H:i:S seems to be the most obvious option but it still doesn’t display seconds. As does this:

{
enableTime: true,
noCalendar: true,
dateFormat: “H:i:S”,
time_24hr: true
}

hh:mm:ss doesn’t work either. I only ever get the same “hh mm” drop-down.