Your basil is flowering early because the plants were pot-bound. To encourage more leaf growth, cut the plants back hard-at least by one half. Simply pinching out a flower will likely just cause two flowers to grow in its place. The hard pruning will cause the plant to branch and produce more leaves. Each type of basil has a certain height at which they normally begin to produce flowers. When under stress, like being root-bound, they will flower much sooner than they would otherwise. They "sense" that they may die soon so the procreation process begins.

Basil is best used fresh.

There is not a certain height that all herbs should be harvested at. As long as the plant is healthy and growing you can be safe in cutting the ones you mentioned down to 2 or 3 sets of leaves from the bottom.

F. DeBaggio

For most herbs where the leaves are used, you can harvest the leaves at any time there's enough to be useful - as long as you only remove one-third of the leaf-growth at any one time, and leave it to regrow before you harvest again. Harvesting is an excellent way of keeping the plant nice and bushy (ie pruning), and with encourage regrowth.

As for the basil, mine flower from tiny seedlings and just never stop - and I grow mine in the garden. It's easy enough to remove the flowers while the plants are tiny, but once they get to mature size, I get out the hedge-trimmers! Your little babies are ready for harvesting already - but you won't get much from such tiny plants.

If using the plants for medicinal purposes, there are sometimes optimal times for harvesting. For culinary purposes, I just harvest whenever I want some!

Catnip: Leaves and flowering tops should be harvested when young, in late summer when the plant is flowering, before the flowers turn brown. Dry for future use.

Chamomile: Remove flowers when they are in full bloom, when the white rays are beginning to turn back from the central yellow disc, with the stem tips and allow them to dry. If the flowers are infested with insects (a common problem), spread the flowerheads on a baking tray and bake at about 60C for 30 minutes, then sift carefully through a colander.

Basil: Harvest at any time, however best flavour is obtained if the leaves are cut as the flower buds show and if flowerheads are continually removed.

Mint: Pick leaves as required throughout the growing season to use fresh, or in summer before flowering if for drying (cut back 3-6cm above the soil line). The edible flowers can be harvested as required. (You can harvest mint as much as you like, any time you like - nothing short of an atomic blast will kill it, IMO!)

If you want your plants to grow to optimum size, you'll need to provide them with space to grow and spread. Teensy little pots won't allow that. My basils get well over a metre tall, and can be twice that in width - that'll give you some idea of what to expect - so you'll need to put your plants into pots which will accommodate a large plant - or put them out into the garden for complete freedom.

Thanks! That was very helpful :)