I can see several problems with this. For example, I might physically place a cache in March, leave it till the end of April before submitting, and then it actually gets published in May. Which is the actual hide date? The default is the date when the cacher created the hide page, but some cachers may change this to the date they physically placed the cache, whereas others, like myself, change the date to the date it's published. Also some cachers may change the date to something completely different, for puzzle purposes.