Final answer:
The question is likely a misunderstanding, as pi, which is a mathematical constant representing the ratio of a circle's circumference to its diameter, does not change at any part of the day.
Step-by-step explanation:
The question, "Which part of the day is usually best for Pi?" seems to be a mix-up between two distinct concepts as pi is a mathematical constant rather than something that varies throughout the day. In mathematics, pi (π) is approximately equal to 3.14159 and represents the ratio of the circumference of a circle to its diameter. It is a constant number, meaning that it does not change at any part of the day, under any circumstances.