How long does it take for China to go to the high seas?

Different ships have different time, 5- 10 hour.

The land extends for 200 nautical miles, which is the high seas. Generally, the speed of cruise ships is relatively slow, about 20 nautical miles per hour, and it takes 10 hour to reach the high seas. A faster passenger ship takes about 40 knots to get out of the open sea.

In international law, the high seas refer to internal waters, territorial waters, archipelagic waters and ocean parts outside the exclusive economic zone that are not subject to the jurisdiction and control of any country's sovereignty.