That's true for software that cares about the location of celestial bodies. In those cases use UTC by all means as event markers. That allows you to count calen

That's true for software that cares about the location of celestial bodies. In those cases use UTC by all means as event markers. That allows you to count calendar days. However to calculate the duration between two dates down to the second you will still first want to convert to TAI to get the correct answer.