The only possible reason why a 1st of September airdate would make more sense, has nothing to do with what any other channel is doing. In the UK Saturday the 25th of August would fall in a bank holiday weekend. Airing it one week later means it no longer airs during a bank holiday weekend.
Why would it be better for it to not premiere on a bank holiday weekend?
Good question. Especially since Let's Kill Hitler aired during the bank holiday weekend last year.