Minimum seeding time refers to the least amount of time BitTorrent must spend seeding a completed torrent before it is allowed to stop it.
Minimum ratio, likewise, refers to the smallest ratio BitTorrent must get on a torrent before it is allowed to stop it.
They might not mean much alone, but together it makes more sense. If you only set one of the two settings, BitTorrent will always stop a torrent when it hits the given criterion. However, if you set both, BitTorrent must meet both criteria before stopping a torrent.
Anyway, there is nothing wrong that I can see, except that you probably want to set a max upload rate to about 80% of your connection's max upload speed, or you will start seeing lots of network lag when you start saturating it. So yes, the possibility that you stated is entirely true, and the simple solution has been posted already. It's normal for torrents to take several months, even over a year, to reach a 1:1 ratio.