The Astro::Coords modules use UTC. For my current project I'm just interested in providing a report for naked eye and maybe binocular observers so the TAI/UTC disparity doesn't matter. The software I use for pointing telescopes does know about such things, but I don't have to worry about it. Much more important is to remember that the software's default epoch is JNow which is almost never correct and that I have to bludgeon it into using J2000 to get things pointed correctly!