I mix all the solutions within a few minutes, but usually the developer first since that is the one that is temperature critical. I'm sure you are right about SS graduates being fast, but I use plastic measuring cups because they are cheap and effective. Done all this so many times that I have a sense of what it will take to reach the right temperature. A half hour or so of temperature compensation after mixing does not seem to affect the potency of the developer.
I realize this doesn't sound scientific enough for purists, but that's part of my point. It doesn't need to be super-scientific or "CSI mode" to get good and consistent result.