Do you have to be married 10 years to get half of your spouses 401k?

Not in Colorado and probably not in most states. In Colorado property the marital part of the current value will be divided "fairly" - that does not automatically mean 50/50. The marital portion is what was contributed and earned during the marriage. How that specific account is to be divided has to be answered in connection with evaluation of the overall property settlement because there is no requirement that each and every asset be treated the same.