You just need a Colorado ID. You can get one for like 12 bucks, just a regular state ID not necessarily a driver's license. You can go to the doctor's at any time before you get it, but the application has to be mailed in within 7 or 10 days of seeing the doctor. There is no length of residency requirement, only a current residency requirement. If you have an ID listing your address you're considered a current resident, the less than 3 months thing won't be a problem. Just make sure you have an ID within 7 or 10 days after getting your recommendation from the doctor because your doctor recommendation has a very short shelf life.