Matcha is an all-day beverage in Asian homes. Which means you can drink it in the morning, afternoon and after dinner. It is also used to help with focus, and deal with anxiety. So if you're feeling a little frazzled or sluggish - have a cup!
Just a word of caution - because matcha boosts the metabolism if you have it on an empty stomach (i.e first thing in the morning) you might feel light headed and even nauseous as your body gets used to its concentrated nutrients, benefits and digestive/cleansing abilities. Maybe add some honey with your first cup, or delay it until after breakfast.
If you are worried about being kept awake at night, rather avoid drinking it at night or have a 1/2 serving so that you still benefit from the fat digestion, curbing appetite and cleansing benefits.