Depending on where you live, you could have 2-6 weeks left before harvest for certain varieties.

I live in new england and i should have about 2-3 weeks until harvest, but im basically waiting for about a week or two before the first frost.

If you wanna get technical about it, you can get a 30x magnifying glass and look at the trichromes, and when at least half of the trichromes are amber in color the bud is ready.

And to anwer your question about snipping them all at once, it probably better to do just that because all of the buds ripen at the same time.