You might want to (once in a while) keep track of where the time went on a particular day. Just like with money, if you get $100 out of the ATM, you might wonder two days later why you have no money left in your wallet. You could figure out where you spent that hunnard bucks if you had a small notebook with you at all times and kept track of every cash purchase.
You might be surprised where that time went. You might have had an hour where you got a whole lot done, or another hour spent waiting around and not getting anything at all done. The 12 hour day might have been 9 hours, with some "dead time." There's nothing wrong with that, except that you might want to know. Once you know, you can figure out if you need to change anything in how you manage the flow of time during a particular day.