for my M&G, we waited backstage for about 45-60 min. depending on who you win your M&G passes from, you'll be put into a line/group (ex: verizon line, burger king line, chevy line..) this is because they need to change the backdrops for every company that is sponsoring the tour.
so you wait in line, then the boys come out, & girls start to go crazy! the boys look around and wave, and the first people in line go up to them. they give them hugs/hand shakes. then they turn around, snap a quick picture, and say goodbye & go.
when i was up next, i tried to hand my camera to a lady working @ the M&G so that she could take the picture with my camera, but she refused and told me that the photographer had to take the picture. so, i went up to the boys, shook hands with kevin first, & he gave me a big smile and said.."hey, im kevin, it's so nice to meet you!," then i moved on to nick. he was like.."heyy," he took my right hand with his left hand, placed his other hand on top of my hand, shook it, and gave me a huge smile! then i went on to joe, shook his hand, and said hello. finally the photographer said it was time to take the picture. i went in between nick and kevin, my friend went between joe & nick. the photographer counted to 3 and then took the picture. after the pic was taken, kevin was like.."thanks so much for coming! we can't wait to see you again!" then kev like rubbed my back, & my friend said that joe rubbed/patted her back.
then we had to grab our stuff & leave the area. but yeah, that's the basic jist of the meet & greets. they're very brief and quick.