In Spanish, the time of day plays a significant role in determining whether to use the formal or informal form of greetings and expressions of respect. The traditional division between morning (mañana) and afternoon (tarde) is not strictly observed, but rather, there's a gradual transition from formal to informal as the day progresses. This is reflected in the different forms used for 'good morning' (buenos días), 'good afternoon' (buenas tardes) and 'good evening' (buenas noches). However, it's essential to note that even during the same time of day, such as lunchtime, you may use 'buenas tardes' with a stranger or someone you don't know well, while saving 'buenos días' for morning greetings. The formal form is generally used in more formal settings, business meetings or when addressing people you don't know well, especially if they are older or in positions of authority. Understanding this nuance can help you navigate social situations and show respect in a culturally sensitive manner.