The 10 mins window (in fact it’s 23 mins) is the window in which she went missing.
9.10 seen in field, 9.20 phone signal puts the phone the area of the bench, 9.33 dog, phone and lead/harness found and no NB.
In actual fact, if she didn’t fall in the river there’s a considerable window of time between 9.10 - 10.50 plus until the police came.