Good answer there for the hours. With reference to months and years, I have a rough estimate but I could well be outdated in my knowledge of the training pipeline... To get qualified on a Herc or C-17, for example...
IOT - 8 months
EFT - 8 months
45 Sqn - 8 months
OCU - 2 months (???)
Now factor in the hold times, which nowadays are very long... it could be anywhere up to 3 years...