It depends on how high the level is when the final peak happens.
Take that number, and halve the value every four days until it hits 500, that’s how long it will take.
So if it’s up at 2000 then in 4 days it will be 1000
Four days later it will be 500. Four days later 250.
If it’s up at 15000... it’s going to take a lot longer.