This time what you describe sounds a little bit like Time Traders, where -- early in the book -- a young criminal is captured and given the alternative to participate in a government project. He undergoes specialized training for what turns out be to time travel. Russians, Americans and aliens tangle in pre-historic Europe.

In Secret of the Lost Race, a young casino dealer is shanghaied to a primative planet. Unbeknownst to himself, he is the fruit of a union between a human and an alien, and is pursued by both reactionary elements of the government and those who want to promote positive contact with the (benign) aliens.

But I still can't think of match to the bit about being deliberately outcast until the time is right.