Good advice from Jack on when to buy what you need to buy.
Honestly, if you plan to keep an iPhone, an iPad, or a Mac for a few years, when you buy means little. If you are in a position to wait for the latest and greatest, it could be a long wait because everything gets better next year. You would always be waiting.
I’m waiting on new iPhones, new Macs, new iPads, and a new Watch.