Is there enough time for SPECIATION for million species

[drkfuture]

I wud like to know if speciation really occurs (trans-speciation), Have we had enough time for millions of species? The slow changes in traits in organisms, taking tens of thousands of years to yield a visible change in variation as evolution suggests, does eventually trap yourself in to a problem of "Time Riddle" - you just dont have enormous enough of time at hand for all these species to come into being. A quick average time calculation suggests that you should have a new species come into being every 15-20 yrs [just rough average time estimation suggests that in about 1 billion yrs ~50 million distinct species evolved]. Though I believe in evolution but I cant understand this part.