When a big Fund or Whale intend to sell and LIQUIDATE a big Chunk of its soon-to-be-worthless Bitcoin - it OPTIMIZES the time and day.
The smallest participation in the Market is of course on Saturdays and Sundays when almost all the Institutionals are closed.
Then The price reaction to a big sale will be the least on weekends.
This IS A REPEATING trend - BIG BITCOIN SELLOFS start on weekend.