The literature on Microsoft TTD [1][2] indicates it is a instruction emulator full-trace approach. It is a little unclear if it is a basic emulator or a instrumented JIT approach, but the reported ~10x overhead is more consistent with a basic emulator. Though maybe their recording implementation is just inefficient causing such excess overhead.

[1] https://msrc.microsoft.com/blog/2019/05/time-travel-debuggin...

[2] https://www.usenix.org/legacy/events/vee06/full_papers/p154-...