Generally speaking, McDonalds restaurants tend to be busiest during breakfast hours and lunch hours on weekdays. This is likely due to the fact that many people are rushing to get food before work or school. Additionally, weekends tend to be busier than weekdays at McDonalds, especially later in the day as people are out and about running errands or enjoying leisure time. Late nights can also be busy at McDonalds locations near bars or clubs, as people often stop for a meal after a night out.
Of course, there are always exceptions to these general patterns depending on the individual location. For example, a McDonalds near a hospital may see more business during dinner hours when visitors come to see patients or staff members take their break from shifts. Similarly, a location near an airport may have more customers throughout the day as travelers have layovers or look for a quick meal before their flight. Ultimately, it varies greatly from place to place and you would need to ask someone who works at that specific location what their busiest times are in order to get an accurate answer.