I feel like it has always been night time for me for strategic tasks because I have the creative space, and especially the TRANQUILITY to think profoundly and clearly.
However, I prefer the day time for 'work that needs to be done', especially within deadlines like excel sheets, payroll for our employees and anything mundane.
Honestly, it fluctuates. Sometimes it's the early morning or late at night (More often in the morning, however). Whenever high levels of productivity present itself I make sure to ride the wave as long as I can!