When Ms. Frizzle and her class evaporate into the air and travel, the geography suggests that Walkerville Elementary School is located within the vicinity of the Appalachian Mountains.
This is the first time the class is shown visiting another country, and the first time time zone differences are brought up. In this case, they travel across the Atlantic Ocean and splash into a puddle of water in London in the United Kingdom where it's 3:00 PM in that time zone. It would appear the class evaporated sometime before 10:00 AM in their own time zone where their school is located as the geography suggests.
This episode is loosely adapted from the very first book in the franchise: "The Magic School Bus At the Waterworks", published in 1986. The following characters in this episode did not exist yet in the book it's based from: Phoebe debuted in the second book "Inside the Earth" in 1987, Ralphie debuted in the third book "Inside the Human Body" in 1989, and Carlos and Keesha debuted in the sixth book "In the Time of the Dinosaurs" in 1994 the same year this TV series first premiered on the air, and Ms. Frizzle's class is shortened to eight students which excluded the ones whom served as background characters in the books.