Mark, yes I would plant, unless you have plenty of space in your propagating area, and the plants are in large pots with the chance to grow more.
Otherwise they are better in the ground, it will be warm by day. Tomatoes are more hardy than aubergines etc.
As so often, advice is given without a reason: before flowers set is good, or if there are little fruits I would cut them off as plants need energy to settle and grow when recently planted, not to go straight into fruiting.
