I've discovered that best time to do yesterday's hardest things that you decide to put off until today is early in the morning. When last night it seemed like a huge, highly challenging task, in the morning, it seemed a lot less. Same work, different time, different perception, different results. Isn't human psychology weird? But that's how it works.
Think of your days as an ascend on a hot air balloon with yourself and weights on it. It'd be wise to throw down the heaviest weights early during the flight. Makes sense, doesn't it? The earlier you get rid if the heavy weights, the lighter your journey will be. Same as the heavy tasks you hold in your to-do lists. Get rid of them earlier, and the easier your day will be. Some people put off the biggest tasks for the last. Hoping it will suddenly disappear or seem lighter at the end of the day. Well I'm here to say it rarely will!
So do your biggest tasks in the morning. There's something magical about the morning, don't you think? I think everyone loves the morning, it's the starting of a brand new day. No matter how miserable yesterday might seem, today we can start the day with happiness. It's scientifically true. The morning is where your cortisol (a.k.a your 'stress hormones') stays at its lowest levels of the day, and even light exercises can boost your endogenous endorphins a.k.a your happy hormones (source: http://www.ca-medicalnews.com/tag/endorphin). So wake up early, do a little stretching, enjoy the sunrise, (if you're a big fan of coffee like me, enjoy a shot of espresso too!) and go get those hardest works done!
Here's a song by Norah Jones called 'Sunrise' which is a great song to enjoy your morning with: