According to sources, the date and time difference is the same in each of the countries, although the current time difference remains the same. For example, let say the time difference between China and Russia is one hour, once the summer solstice happens in china, the same thing will happen in Russia an hour later. Generally speaking, the summer solstice happens twice a year.
This year summer solstice happened in the US on the 21st of June around 15:54; the December summer solstice is predicted to occur on the 22nd around 04:19. History has it that the summer solstice has been seen as one of the most significant times of the year, and it is marked by rituals, festivals, celebrations, and in some places, holiday. However, in most countries’ calendars, it is regarded as the beginning of summer.