Well, it's set in 2273, but at the time it was written, going by the Chronology's estimates, that was assumed to be 2 years after TMP, and there are references in the text implicitly consistent with that. (Mainly concerning a recent switch to new uniforms, which Howie presumably meant to be the TWOK-style ones.) But then VGR established that the 5-year mission ended in 2270, which required TMP to take place in '72-'73, so TBM ends up closer to TMP than was assumed when it was written. But it still pretty much works that way if you're flexible about a couple of early details.