Since U4 there’s a significant performance improvement for importing ACMI .flt to .vhs. which reduces the time needed for import by at least a factor of 10 to 20. If you’re using the latest version of Tacview, I would recommend to set the ACMI file size to 50 MB, because you are much quicker at the debrief screen and you can merge the individual files without any problems afterwards. 😉