Dan has explained so all I'll do is add that it's the sort of thing Sherlock Holmes used to do with the footprint of a person! As for the time of day, perhaps prints made at night, or in the cool morning dew, might be different for those laid down under the hot noon sun. I suppose if I trod on a bat it might be clue I was out walking at night. Hmmm?

I think it means that some people can look at a deer's footprint and tell what time of day the footprint was made, and what the weather was when the footprint was made. For example, a footprint made in wet ground might be deeper and less distinct than one made in dry ground, so someone might be able to look at it and say "It's dry now, but it was raining when the deer made the footprint." How anyone could possibly tell the time of day when the footprint was made, I don't know, and I'm not sure I believe it.