>>13720669, >>13720559, >>13720728, >>13720738, >>13720751 M7.4 Earthquake - Southern Qinghai, China

At 3.5 feet per second, if the earthquake made a wall of water, 784 miles to the dam it would take:

784 * 5280 = 4139520 feet.

Divide that by 3.5 feet/sec, to get 1182720 seconds.

That's 328.5333 hours, or just under 13.7 days.

My math could be off, and the river probably doesn't flow at the same rate in all spots. Flow rate from https://www.britannica.com/place/Yangtze-River