It seems that there is a timer on the gnome game, which I read about on addicts. Here is a pic when I had finished a game in my town (you can see the timer at the top):
http://i.imgur.com/Bkamst4l.jpg
You will get less loot if you don't finish the game in the time.
Large offerings look like a better ratio that the small or medium ones. Someone in another thread suggested a ratio of 1 item for 5 antlers (which is the case in my 2 examples for the small and medium ones) but the large payouts are higher.
http://i.imgur.com/k0Iwyuhl.jpg
http://i.imgur.com/JCW2qErl.jpg
