Basic SEO
 

It's said that it needs some time before you see the actual effects (positive/negative) of changing specific SEO things to your blog, but how long is that interval usually supposed to be?

1 week, 2 weeks or even more?

I think you'll notice the effects in 2-3 weeks. In meantime don't change anything ;)

shouldn't take too long with G updating as frequent as it does nowadays.

from one to six months

it is subjective.....may be less than a week or more that a month....

From what I have seen it is gradual, and it will improve in about a week and upto 2 months.

lately a couple of days and you will see a difference

I love the fact that a whole bunch of obviously smart people just had completely different answers. Fuck you, Google.

Yeah, I feel like going to 5 different doctors and getting 5 different diagnoses :1orglaugh

For real it depends. Answer following questions:
1. How often google bot revisit your site? How often google bot revisit each page of your site?
2. How old is your site?
3. What kind of changes did you do?

To guess when changes take effect is unreal, usually it takes from 1-2 weeks to 2 month. But again, it's individual for every situation.

Advice: Don't masturbate on each unique user came from google, better spend this time improving your site: add more and more and more hq content.