Pricking out toms

I do prick out once the first true leaves appear, but also move things off the heat mat as soon as germination has started to stop them getting too leggy. It feels to me (no scientific evidence, just observation - assuming the memory is right!) that everything is a little slower to move on if pricked out any earlier.
But having had no germination of Gardeners' delight last year I sowed all of the packet this year and of course now have a pot full of seedlings. I'll do some now and leave some until they have true leaves and then see the difference.

I ended up with three pricked out at the first true leaf stage and three at the seedling leaf stage. By the time of planting out I'd lost the labels  so didn't know which was which, but as they were all the same size I guess it didn't make much of a difference.