I think you can specify any length of time that you want on GR. I've seen some run several months. On LTMG it looks like it is one month max. My personal preference is no longer than a month, but two or three weeks is better. You could always try a couple of different time frames to see what works best. I don't know if a longer time frame would necessarily kill interest in the book. The reader enters the giveaway and then just waits. It goes into a list of giveaways they have entered (on GR...I don't think LT does this for the MG giveaways) and they can check it at any time. I just don't like the longer ones because I'm impatient
