I had a chance late today to check on the dippers.
In 20 minutes of observation I saw only one adult who spent over 5 minutes preening before heading off upstream. It came back and fed once. Then went back up to the nest box and removed a fecal sac. Then took its position under the nest preening. I looked under the bridge and did notice a dried plant stem protruding from the nest entrance which seemed a bit odd. There may only be one nestling inside the box. It likely hatched between may 15-20.
I then visited Main St. Bridge and saw both adults and saw the male feed. There seem to be 2 nestlings. They are likely less than a week old.