>Because it has units of time (seconds, often) and it's done using time-stamps, as in begin-time and end-time. If you are recording a duration you have another

>Because it has units of time (seconds, often) and it's done using time-stamps, as in begin-time and end-time. If you are recording a duration you have another unit. If you use begin-time and end-time you are calculating a duration, which is different of course. If you calculate durations, then you might consider leap seconds, if they are important for your measurement. If not, then you just ignore them. I don't see a problem here. Besides, leap-seconds are known, so removing them from a calculated duration is not a problem.