It's totally true that tomatoes need warmth to grow! While I haven't dared start a tomato from seed yet, last year all three of my tomato plants did the same thing -- they sulked and pouted and wouldn't grow in early summer (which around here is late May, early June-ish) but as soon as the hot weather hit at mid/end of June, you could quite literally SEE them growing, if you just sat out there near my plants. In one week they grew two feet!!! Just because it was the right (ie, *warm*) weather combo for the plants.
I was fascinated by the fact that I could measure them at one height before I went into the house for the night (at 11', say) and in the morning, they were taller (typically they'd grow 2-3" overnight).
The zukes were the same way -- once it got warm enough, I had to watch those things like hawks! Occasionally I'd go out in the morning and I'd see a baby zuke, when I came out again that evening about dusk, the same zuke would be about 8-9" long and ready to eat.
The right temp is very important for tomatoes! That's the biggest thing I learned with my first garden attempt last year. If you get the temp right, whether through chance or design, you'll see a lot going on in your garden
Mine took forever to ripen, though, I finally had to bring them inside.
Whitewater