I would say 'all of the above'. Craigslist is such a major vehicle for searching for homes to rent or purchase that with the sometimes hectic and varied lifestyles of Denver residents someone is looking all of the time. As far as best times I would say Friday night to Saturday morning is one of the best times of the most traffic.
Be sure and monitor your home listings, refresh them, and watch for scam 'clone' listings where crooks are using your information to bilk money out of unsuspecting buyers. I have seen vacant listings where scammers went in and held open houses on the weekend and on the 1st of the month several moving vans pulled up to move in. All had given substantial 1st and last month rents and deposits to scam artists who represented that they owned or managed the property. Hope that helps.
Robert McGuire ASR
Your Castle Real Estate
Direct - 303-669-1246
Also, Craig's List will not most of the listings on the other two websites, as it is a separate place to advertise. Lots of for sale by owners, etc.
Let me know if I can help further. Julie Montgomery, RE/MAX Masters, Inc., Littleton, CO