Kindergarten teacher here!
To help your child kind of understand when the pool MIGHT be done do this....
Print out a year calendar. Circle today with a green color. Go about 3 weeks over from when the PB said your pool will done and circle it in blue.
Hang this on the fridge and allow your child to put a red x on each day when they get up in the morning. That will help. It gives them something concrete to look at.
You can make it in to a lesson about day/night, how many hours in a day, how many mins. in an hour. You can even go into the rotation of the earth and how we get day and night.
I wonder if you show the calendar to your PB if he will make sure he beats his time line?????? LOL
Kim