Radio Shack has been spotty about carrying those pocket scopes in the stores, so it's hit or miss. Ganga is on the money about when to harvest and how to tell. Using a scope to look at the trichs is the only reliable way. I prefer when they are almost all cloudy and the first 5-10% are going amber. You can alter the high somewhat by when you harvest, with more of a cerebral head-high earlier and more of a couchlock body stone later, but you won't be able to get a sativa-like high from a pure indica or vice versa -- the timing gives you some control within the range that the strain is capable of.
I'd say at least 7-10 days. But thats obviously just from looking at the pics. I got the famed radio shack microscope before I harvested last time and very happy I did. Its kind of a pain in the ass to use but worth it. Post back with some harvested weight!
You could probably print out that webpage, take it to your local radio-shack and ask them to get it for you.