It's graded vesting, I've always seen it at 5 years (20%/year). It seems they do 20% after the first year then 1/48th afterward monthly (which is nice).
Legally they can do up to 6 years.
Legally they can do up to 6 years.
All the tech companies I've seen use 1 year cliff/4 year total vesting. Ie, 25% after the first year, 1/36th of the remainder monthly.