Does Colorado law require employers to recognize this?
No.
Are they required to accept the common law spouse on health insurance if the employee requests it?
If the insurance contract lists common law spouses as eligible dependents, and if the request is made within the time frame the contract requires, yes; otherwise no. Note that the exact wording of the contract is important; they need not necessarily list common law spouses specifically if the wording indicates that all spouses are eligible.
Also, if the employer drags their feet, is their a "reasonable amount of time" that the request must be satisfied by?
Assuming that common law spouses are eligible for coverage to begin with, I very much doubt that there's a specific number of days or weeks that the employer has to complete the request. However, they cannot "drag their feet" beyond the length of the time the employee has to add a dependent.
What I mean by that is, NO employer is required to add a dependent, be it a common law spouse, a son or daughter, or any other dependent, to the insurance plan except at certain, specified time of the year. One of those times is when the employee first becomes eligible for the insurance; one is during a month long "open enrollment" that happens once a year at the time of the insurance renewal, and the final time is within 30 days of a "qualifying event"; marriage, divorce, birth, adoption. No employer is required to allow, and in many cases may not legally allow, additions or subtractions of dependents at any other times. That applies not just to common law spouses, but to all dependents.
Say open enrollment is the month of April. If the employee applies to add the common law spouse on April 1 for a May 1 effective date, the law doesn't say the employer has to have the common law spouse added by April 5, or April 14. But the employer can't let it go beyond April 30, because on May 1 the employee's right to add the common law spouse expires and does not come back until the next April 1.
