I don't know what part of Colorado you live in and I don't have an automatic sprinkler system so have no first hand experience with it, but I would definitely not be turning on my sprinkler system quite yet. We will continue to get freezing weather for at least another month, I would say. Probably the earliest time would be in mid-April. If your system was installed by a commercial landscaping/sprinkler system company, why don't you ask them, or ask the folks that came out to winterize the system last fall?

I believe the average last day of frost - which is a light freeze - here in the Denver metro area where I live, is at the end of May, actually. I have linked a chart for you that may be of use - or you could call your local county extension office.

Holly

Here is a link that might be useful: Average 1st and last days of frost by city, CO