Yeah, but on ship this size 400x60x0.2=4800 tons of difference! I'm somewhat exaggerating because ship hull isn't cuboid, but it is still likely equivalent to removing around hundred containers.

Only a portion of it was grounded, not the full length of the ship.

Someone linked a BBC article stating that they shifted 27,000 cubic meters of sand, so there you go, they could likely remove a meter under the whole thing in a similar amount of time (probably longer to cover area instead of digging down, but that isn't what they would need to do).

Good thing we are talking normal monthly tidal variations (not seasonal) which vary by meters, not centimeters.

Not in Suez though.

Yes, the high tide is a better opportunity to do it, the tides over the next couple of weeks are still within 20-30 cm. The worst day in the next 30 days is 60 cm below the highest.

But maybe the dredge only made a few centimeters of difference running for 5 days, who knows.