I'm not saying it necessarily should be preferential, but starting with groups first would be less of a headache. It's like putting sand in a jar first and then trying to fill it with rocks. You put the rocks in first and the sand will slide between the rocks to fill the jar. It's the same with individual people and groups for reservation times. Accommodate the big groups first so you can gauge how much space you have left for individuals. I hope that makes more sense.