On my timeline, I actually had the shop class scene on September 12th. I know Peter tells Ned he'll see him at school tomorrow, but I feel the 12th is more logical than the 10th. It places the scene on the Monday after the Friday party which should be their first day back at school, Ned talks to the kid at Chess Club where we can see a poster that they meet on Mondays, Wednesdays, and Fridays, and it places Peter finding out he can use the decathlon to investigate Toomes men the night before the team leaves. This makes sense with him asking at the last minute to rejoin the team as it would be the following day.
The line about seeing Ned at school tomorrow could be chalked up to another case of the movie not paying attention to the timeline (just another example).