The last upgrade class was 10/02, the most junior pilot in there being me, at two years. I don't think there is any realistic way of predicting future upgrade time due to J4J and an unknown number of total aircraft to be delivered.
Also, according to the company memo regarding the 210 new-hires, it said that the only method for applying right now is by internal recommendation from current pilots. Not that it's set in stone, that's just what it said.