mj, you are looking at an unuseful chart. no real TA possible with it!
use this:
http://stockcharts.com/h-sc/ui?s=XRM&p=D&yr=0&mn=3&dy=0&id=p18357245594to your question: you can draw trendlines whenever you want! no minimum amount of days. just use your common sense, if a trend lasts for many days you know its a strong trend. but if you just draw a trend for 2 days you may imagine it has not much to say.