Whatever time you decide on, be sure to stick with it. Let your members plan their schedules around reading group, rather than trying to fit reading group in around everyone's schedule. Unless you're sponsored by a bookstore or library, the next thing you'll need to decide is where you'll meet. The most popular option is to meet in members' homes, rotating turns at hosting. Your meeting time will help determine snack options for your group.
Some groups choose to meet in restaurants.
Be sure to find one that has tables large enough to spread your books out and that doesn't mind your group staying for discussion after you finish eating. Perhaps a little wine and cheese will enhance your discussion. Another aspect of reading group you'll want to consider in advance is the format your meetings will take. Some groups find it helpful to hire a professional leader, at least to get started. Contact your local library or bookstore to find out if there are such people in your area.