Local Area Business Committee - What is the best meeting time, during or after work?

Our charitable organization is inviting several area businesses whom we have worked with before to a committee that is focused on helping build community participation in two of our annual events. This companies participate in some capacity, but we're hoping they will essentially help us spread the word about the event. The meetings are only once per month for one hour each, and they have the option to conference call. I am wondering what would be the better choice, to host the meetings during the business day, since the participants would technically be representing their business, or to host it right after work, so their participation does not affect their work load.