This guy mastered and mixed my hip hop vocals the mix is not as I wanted and the mastering seems ok. How much is fair for me to pay him for his time?
Well, considering you haven't told us how much he actually mixed/mastered, how much time he spend doing it, and the fact that he hasn't finished his job yet, how much to pay "for his time" is an impossible question to answer.
But when the time comes that he actually finishes his job (i.e. actually gets mix approval from you before he "masters" anything), you might want to look at it this way. I don't know what state you're in - or even if you're in the U.S. - so, just for example, let's use the federal minimum wage as the base rate to pay him. At $7.25 an hour, you can calculate it this way:
Since the guy is an amateur (or is he an armature?), and since he did not state any rate or come to any agreement with you beforehand, and since everyone involved in this transaction is operating without a clue, I'd take that minimum wage and multiply it by zero, and then multiply that by the amount of time wasted. That will be the final bill, with the only profit to be made in the learning of the following lessons:
Anything worth doing is worth doing right.
Anything done right is something worth paying for, and probably won't be cheap.
Anything not worth doing is not worth doing. Anything not done right is not worth paying for.
G.