Time, as in the time of the day, is a social construct. The sun doesn’t know, nor cares, about going down every day at 6 o’clock. It is not just a human construct because we use it as a tool to coordinate our activities with each other, which makes it social. As many other people have thought before I also think: why doesn’t everyone just use the same time? Just throw timezones and the politics behind them out of the window and just choose one for the whole earth (UTC is a good candidate for this). Many people that have to work with people from other countries already use UTC. Because it is easier.
Due to having timezones, we can talk about a time of getting out of bed. Someone in Perú, for example, gets out of bed at 7:00, whilst someone in 中国 (China) does it too at 7:00, both local times. They have that in common. And they, with everyone else, have the culture of doing certain things at certain times of the day which sometimes coincides with other cultures. But what would happen if everyone used the same timezone? For example, in one country people would start their workday at 0:00, whilst in another they would start theirs at 9:00. So if you ever travel from one country to another, you would have to know at what time shops open and close, which wouldn’t coincide with the times you are used to in your country of origin. I want to be clear on this, I’m not suggesting that everyone should do things at the same time, people would still go to bed, for example, at night, just the exact hour would vary. Some people would be used to seeing the sun in the middle of the sky at 12:00 and others would find it there at 18:00. We would be detaching the social construct that is time from actual physics which is the sun in the sky.
For many people, the day would change in the middle of the, well, day. For example, currently, the day goes from one to the next in the middle of the night, that’s something the whole world has in common. If we all used the same time then for some people the day would turn from Saturday to Sunday in the afternoon, while being awake. Which, at least for me, that would be weird, and I’m sure for many people as well, but we would get used to it. It would be just something to know for each country. Which we already do with timezones.
Some social coincidences like working from 9 to 5 would just not have any meaning with a universal time. Which I think is actually all right because not everyone works 9 to 5. I don’t. Many people work night shifts, others have to start earlier and finish earlier. This type of cultural association with time would fade away with the change.