Manny, I agree that making the correct moves should be more important than speed. The tactics trainer definitely puts too much emphasis on speed.
Tactics Trainer too sensitive to time considerations
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I can't confirm this one 100% but I did run some tests.
In a two move tactic if I make a correct move then immediately make an incorrect one I'll score something close to zero (I assume it depends on the rating of the problem). If I wait until the time runs out and then make the correct move, I'll score much worse.
I can't see how the correct move should ever score lower than an incorrect one.