Duane's novels move back and forth from a Phase II
-style (as in, the aborted series, not the fan films) pre-TMP 2nd five-year mission to the end of the TOS five year mission and then to a post-TMP second 5-year mission. They tend to keep their internal chronology, but where they fit moves depending on the editor at the time. I pictured Doctor's Orders
as being set in the TOS era.