Actually, dont worry about the 3 seconds rule. It isnt a rule like that. It is there to make sure you reduce AA by not thinking too much. (No, Rune, I still disagree!

).
So what you really need is to stop worrying about it and stop worrying about faliure. Every set is different so you need to learn how to calibrate. If you cannot do it now, you will learn from experience. As it is now, I calibrate during my opener, I just need like 1 second to calibrate. What she looks like, how she stands and how she acts gives away a million things you can use.
I have been around for a while so obviously I have more training but dont worry, you will get it too! You just need the experience. I still use my all time favourite, the gay opener, unless I make something up on the spot.
PUA: Hey, quick question, does this jacket make me look gay or is it metrosexual?
You can read a lot from their reaction. But thats not something you can be told over a forum. You need to collect experience. There are a million signals going on all the time, like bodyposture and hand signals and shit. But if I tell you something that is true for one situation it might mean the opposite in another situation in combination with other signals. So you see, it is not easy to tell but way easier to figure out for yourself. Plus more fun too!
Hope it helps.
As for my comment above. You could also say that, yeah, if you love the game but not the prize you might not get pussy. Unless of course you get pussy and realize that it isnt all that awesome. Thats when you can afford to be selective.
Like Hobbit says: You long for sex until you have it, then you realize that it fucking sucks.