Every September Apple unveils new models, and in the first few weeks demand outstrips supply: third-party retailers have no room to discount, so prices stay anchored to the official list price.
Once broader stock arrives, typically within 4-6 weeks, competition between retailers picks back up and the first genuine discounts start to appear, alongside a growing supply of refurbished units from the previous generation.
Anyone who can afford to wait even a month and a half after launch tends to end up in a stronger negotiating position: several retailers competing on the same model, rather than one fixed price everywhere.
Once again, comparing prices across multiple retailers is the most useful tool here — not to guess the perfect date, but to see in real time when competition between stores actually starts moving prices.