Rules v. Situational Ethics

Write down everything you'd like to do in a day; you don't have any obligations, just write down everything...a trip to the mall, waking up and brushing your teeth, taking your dog for a walk; whatever it is you do, just jot it down.
And so I began to make what would become a foundation for my life, a fundamental anchor for the day, holding me steady through the angry white caps and the calm ripples. She called it, "Your Perfect Day", and it sounded great. You could do whatever you wanted for that entire day, time and money binding, yet this day was absolutely yours.
I couldn't help but smile, because this was awesome. The freedom to do everything that you want to do in your grasp. Of course this was eighth grade home and career skills, so nobody took the teacher or the assignment seriously, but a couple years down the line, I found myself coming back to this idea. It was different, it was radical (at least organizationally) for me. I created a daily schedule, "My Daily Schedule", and I intended to follow it to the t. I incorporated everything that was mandatory: breakfast, school, dinner, homework, sleep, waking up; and then I took what I considered important to me: practicing my sax, reading, etc. and thus created a master schedule. It made perfect sense; just follow the schedule and you get everything that you need or want done in your day. Just follow it to the t...well, that didn't go over so well.
Theoretically, my schedule was perfect, but realistically it had some faults. Some mornings I woke up late, or it was simply raining out so I couldn't go out for a run, or I had a rehearsal; whatever, something always came up or messed with things. Thus, with Murphy's law in full effect, these new situations provided obstacles for my daily schedule. In order to undertake my "Most Efficient Day" (My Master Schedule), I would almost always have to change or adapt my schedule to the new circumstances. However, this proved a breach of moral: in order to adapt to my situation at hand (which after adapting to, would prove most efficient) I would have to go against my word set in stone.
So let's step back to examine the bigger question: At what point does it become okay to change/ignore/bend the rules for certain situations, or is it even okay to sway from the rules? This is a tough question because it in itself poses a concrete law, and laws are meant to be all encompassing, unless otherwise noted. I believe that regardless of circumstances, rules are meant to be set in stone. And by setting these laws in stone one ensures the best, if not, most efficient, means of ensuring the intended outcome of a certain rule. Granted there will be victims of circumstance, but aren't there always? This should be no determent from those who wish to secure the good for their fellow man through a set of concrete rules and laws. Because ultimately, rules pose a necessary and irreplaceable means of obtaining a just (to the greatest extent feasible), orderly, and good society.