In Poul Anderson's works, a "nexus" can be within a timeline or between universes. At a nexus within a timeline, it is very easy for a time traveler or a quantum fluctuation in space-time-energy to change the entire future. Therefore, the Time Patrol polices these nexuses. At a nexus between universes, inter-cosmic travelers can meet and might gain knowledge that would change the entire futures of their timelines. Therefore, Taverner polices the conversations in his Inn of the Old Phoenix which occupies one such nexus. Thus, there is a conceptual continuity between the mutable timeline of the Time Patrol and the multiple timelines of the Old Phoenix.
There are limits both on how long guests can stay in the Old Phoenix and on how often they can visit it. The narrator of "House Rule" suspects that:
"...the hostel exists on several different space-time levels of its own." (p. 65)
- but I do not know what this means or why it should affect guests' visits.
Anderson's Time Patrol guards a past;
James Blish's Service guards a future;
Taverner guards many pasts and futures.
Thus, one man has a bigger job than two organizations.