pre-rut would make sense..the young bucks were probably hoping to find a doe they could mate with come time...for you not seeing mature bucks that could be because they already had does, waited to get there does, or just there were no real mature bucks around...when hunting in CA (blacktail deer) i do find that younger bucks will run with does during the pre-rut and the mature bucks don't really have does or are seen with does until closer to the rut...not sure if this holds true to whitetails but that is what i have seen..