Cilantro/coriander "bolts". That is, it sends up a flower stalk from the crown which is different in character from the rest of the plant. And yes, the flavor of the leaves does "go off" when that happens. Pinching off the flower stalk won't change that. However, the new plants that will spring up in the bed from the self-seeding will be just fine.

Oregano simply starts to bloom. Many people who grow it consider that the flavor is best when the plant just comes into bloom, but you can use it pretty much any time.

Basil is similar to oregano in that it doesn't develop off-flavors. However, being an annual, the plant is going to be mostly done soon after blooming as the seeds start to form. You can delay that by pinching off the flower stems when they are still in bud Some people even use the bud stems in cooking as they do have some basil favor.

Thanks - basil was started later than dill (and of course the oregano and cilantro were already there) so long ways from flowering. I saved some of the oregano sprigs with flowers since they were so pretty but forgot to put them in salad last night.

I was just wondering about the cilantro, don't have anything to use it with just yet since tomatoes are a long ways off. So I'll let these reseed again, hope to have some in Sept? Or should I start new seed now (don't know how long it takes to get from flower to seed to new plant, didn't see any new plants last year after it bolted, in fact never even really saw seed but I'd like to save some this year)?

Cilantro seeds , aka coriander, is an spice by itself. It has totality different ( and IMO better flavor) than cilantro. I buy it from Mexican / Asian / Indo Pakistani stores in large quantities and Plant some of those rather than paying couple of bucks for few grams of seeds.

Regarding the question of : FROM FLOWER TO SEEDS: In my estimation , it can take a few month for the seed become fully ripe and viable. It is better to use those FRESH seeds in the kitchen and buy something else to plant, UNLESS you have a whole lot of them.

Thanks, I was planning on using some of the seeds for cooking but wanted the plant(s) to reseed as well since the original seed is older. I'll plant what I have left now and hope to have it the same time as tomatoes. Hopefully next year I'll have a bigger patch of reseeded cilantro and early tomatoes.