Though I am not against having a hard line of 24hrs after the last sim as Tom suggested, I tend to disagree that you dont know if you want to extend someone until after the final 10 days are played. If you dont know by the first 110 days of the season whether you want to keep a guy another year or not, then he must be very iffy. And its not just keeping him around, its spending valuable (to some) team bank dollars to keep him around. I would think that those 110 days and at minimum 72 games should be enough to tell you about a player.
That is just my personal opinion. As stated previously, I wouldnt be against an extra 24 hours because that would leave an additional 24 hours until the playoffs start. However, I just think the reasoning doesnt hold much value.