I am guessing that the general rules we read for "start this indoors 8-10 weeks before your average last frost date" have to be making some assumptions about your indoor seed starting conditions (optimum?), and also about the speed with which your microclimate warms up.
I wonder if they are also makign assumptions about the size of the cell you start things in, or the number of times you pot them up before shipping them out. Or does everyone just understand which plants need potting up, and which plants can live in a small 6-pack for 8-10 weeks?
For example, say you can plant out one Brassica when nights stay above 25F, or plant out tomatoes when nights stay above 50 (or 55).
In my gradual Spring, that might mean planting the Brassica out 6 weeks before avg last frost, and tomatoes waiting 6 weeks after.
Someone whose Spring warms up faster might have transplant dates only 2-3 weeks away from their avg last frost date.
Am I exagerating the differences in "speed of Spring"?
Or do experienced gardeners just adjust mentally based on thier own successes and failures?
or do the variables of weather from year to year just overwhelm the attempt to predict down to 1-2 weeks what the "best" date is to start seeds?
I'm also thinking that people using cold frames or tunnels must be applying some fudge-factor like "my tunnel gives me 15 degrees of warmth at night, and that translates into a 3-week gain".
How do you-all adjust "the rules" to your own climate and circumstances?