I think it's a 2 year minimum for contracts <=$1m?
There is a two year maximum for contracts of $0.5m.
Here are the rules for minimums:
Item AIX C-2.0
Contract extensions follow the contract maximum lengths as shown above as well as their own minimum standards.
$20m+ - 5 years
$16 to $19.5m - 4 years
$11 to $15.5m - 3 years
$5 to $10.5m - 2 years