Depends on the species, late morning for Mountain Quail (Western Nevada late season) , catch them when they come down to water (much like Chukar). Gambels here in the Southern Nevada desert, mid-morning after they feed before it warms up midday, Valley Quail, seems to have the longest active window, morning thru late afternoon (Idaho hunting) As a kid in Michigan used to get Bobwhites when you could find them...I try to leave any of the birds late in the day when Winter sets in, let them re-covey for their nightly roost. Never could find Mearns in Southern New Mexico..