It is my understanding that the Selection Committee does not consider any national rankings when debating who to invite, even back when there were members on the committee that did publish national rankings.
As for times: I think most on the committee probably realize that cross country times are relative to the course, although there probably is some kind of bias towards favoring faster times, or being leery of weather's effect on the race, but I don't think that is usually going to come into play.
What the committee mostly looks at, I believe, is three key things:
1. How competitive were the teams with the teams ahead of them
2. How tough is the region perceived to be
3. How competitive were the teams with other teams that qualified or are in consideration throughout the year (such as "At Large points" for beating a team that won their region at some meet in late September or later)
I think most would agree the Southwest is very tough, so as long as the #3/4 teams aren't blown out by the #1/2 teams (which they might, as it is a VERY tough region IMO), I would think a #3 or #4 team out of the Southwest will get serious consideration.