I don't know but maybe we are in a timeline situation here. Diane is wearing the same outfit as the day she made the coordinate search at the bar I believe. Does seem to be a long time in Buckhorn.

I don't think they have overstayed Buckhorn and believe their investigation is moving fairly fast.  The Blue Rose Task Force scenes we just saw likely take place early on day 5 of their timeline and I'd bet their next step is to leave town.  Here's my take on the timeline. 

Day 1 - Gordon gets call about Cooper; plans to leave for Yankton the next day; Gordon meets with Denise

Day 2 - fly to Yankton; meet Mr. C.; talk about need to meet with Diane; fly back to Philly; Albert meets Diane in bar

Day 3 - Gordon and Albert meet with Diane in morning; fly back to Yankton; Diane meets Mr. C.; diverted to Buckhorn while flying back to Philly; see Briggs' body; interview Hastings

Day 4 - visit the "site"; back in police station; in hotel for Blue Rose conversation; at 7:28 Diane texts about Las Vegas; at 11:05 Gordon meets with Albert ("What do we know that we haven't asked her about?")

Day 5 - before hotel bar opens Diane searches for coordinates; Albert briefs Tammy on the origin of Blue Rose, Gordon recalls his dream, Diane is asked about Briggs/ring, they call Las Vegas and talk about the call with Truman. 

I would guess that the next Blue Rose scene we see will be the "This is Cole" scene from one of the trailers.  Based on that call, I assume the next stop is either Twin Peaks or Las Vegas.  Even if we don't get back to this story line until Part 16 or 17, it will likely progress at a speed that a major Blue Rose investigation would (very fast).