For some reason, it seemed that whenever they were out of direct contact with Starfleet, the response time was always three weeks. Well, not constantly, but a figure of three weeks or more was specifically cited in "Return to Tomorrow", "The Enterprise Incident" and even TAS: "The Time Trap".
Now that is
interesting. That does make one wonder if even the Constituion Class Enterprise was often no more than a certain distance from Federation space? If the three week thing is a measure of how far away they are from 'home'.
I don't take it as anything more than a coincidence. These were episodes written in different seasons by different people, and somehow they all gravitated toward three weeks as a suitable delay.