I find that when it gets thicker and how long it lasts is a reflection of what's going on inside of me. I came down with a bad cold on Thursday. I pulled on Friday and it became thick immediately & lasted a long time. I gave up and spit it out. My symptoms are going away and it was a "normal" pull.
A normal pull for me is: gets thick around min 5, lasts until mins 7-10 and then becomes thin.