I doubt it makes a difference. Full moon for May 2013 will be the 25th. Sunrise 5:01 am, sunset 8:34 pm, which is 15 hours 33 min of daylight. Night only feeding won't fill the belly. Bears should be moving good by then with the rut starting. If its a hound hunt the dogs can pick up scent hours later. If its a bait set they can hit anytime. Spot and stalk bears can be seen all day. I will say the less direct light the better, overcast is good, the shady side of things will likely hold bears longer. Smaller bears avoid bigger bears so they have to move and feed different places and times. One of the early collar studies in Idaho surprised the biologist how active bears were in the day time. Go, have fun, hunt hard all day, take advantage of the moonlight for getting into, and out of position. I've never seen underwear make much difference wear whats comfortable.