lol - cut and fill on a slope is not trivial. It’s more of an exponential function than a linear one for the amount of material removed the deeper you have to go down. They dodged a HUGE bullet with the highest tides happening this weekend. If they had gone beyond a Tuesday with the drop in tides each day as the moon got further away it would have been sketchy if they could have gotten ahead of the tide or not.
The timing of this couldn’t have been tighter. Thankfully they came out on the good side :)
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).
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.
Of course each meter of depth is a little harder, but not that much harder.