usually i write my posts a day ahead of time and schedule them to post later.
sometimes if i get caught up processing pictures and such, i schedule posts as far as a week in advance. when i do this, i usually schedule them to run at 6AM. sometimes my schedule time is five, because sometimes i just hit the button that way.
any post with a different time on it is a post i wrote the day i posted it, and posted it with the automatic time stamp.
oh, were you LOOKING for the time stamp? i don't think it's in the RSS feed, but if you really, really want to check whether a post is from TODAY, the timestamp is in the lower left corner.