If you don't feel the second dose kick in right away you should probably take a third dose. Surely you won't regret taking a third dose.

Had a buddy back when I was a big pothead, he was always down to push it. He'd call me up, I'd be with a third friend, and he'd be like "Go get three blunt wraps and meet me wherever," and so we'd just do it, and we'd meet him, and he'd be like "I got three different strains, we're going to smoke all three of these blunts." My friend and I would put up the fight, it was customary, but our buddy would say "What's going to happen to you?" And that was always where the fight would leave us, and we'd acquiesce and a smoke three blunts, and we'd get super high and sit in the front bench seat of his Toyota Avalon listening to Ratatat.

I no longer smoke (or use marijuana at all), but I have many fond memories of my smoking days.