Play it safe and allow yourself 3 hours for the round trip. I'm a 42 year old runner, my wife is in good shape and we have two fairly active kids; 13 and 11.We expected to complete it in two but ended up missing our Cog Railway reservation. ( They managed to move us to a later time at no charge.)Street parking is insane at $10 an hour, but if you're lucky, you can park in front of the chateau for 4 hours at $10 total.
Of all the hikes we did in Colorado this trip, this was the least enjoyable. Still beautiful, and the visitor's center was great, but it's not much of a challenge and it's pretty crowded. The drive is lovely and there are plenty of other trails in the vicinity. Unfortunately, lightning kept us from exploring them.
B.Y.O.Paint! It is possible to find some remaining in a can from the ground, but not always.