I wouldn't feel too badly. I nearly wrote a similar post earlier this week.
There have been several later-in-the-day posts about books this week that looked interesting (including "How to drive a tank") but were no longer available the next morning. I decided that the time of a post probably had nothing to do with when the the book became free; it was based more on when someone first noticed the book was free.
I had decided that I need to check later posts or run the risk of missing out. Of course, I neglected to do so last evening. Oh well.