How long do you guys give a new job to fairly judge it?

3.50 weeks

Make a blood pact with the manager that you get half of the embezzlement to keep your trap shut

You should be able to recognize if you've made a mistake within 6 weeks IMO.

3 months should be plenty

3-6 months should give a decent read.

10-12 years

I left one at lunch time on Day 1. I left for lunch and never went back.

Remember, they are feeling you out just as you are them. I would say into the 4th month you should get a true feel.
After two weeks I thought one of my collogues was an arrogant arse. A year later and he is my favorite work friend. He relaxed once he knew I was laid back. Goes both ways.

I would think you would know within the first week. I'm of the opinion that if your gut tells you it is not right, it probably is not. I had a friend who went to work for a mortgage company 20+ years ago who knew on the first day the culture was not right and lasted until Friday at lunch the first week when he went to lunch and did not come back to work. Good move because the company got raided by the state the next Tuesday.

I was at my last job for 8 days before I found my current job. I ignored more red flags than a May Day parade in Havana in the hiring process and almost flipped shite day 1.

Sent an e-mail that pretty much said I'm resigning effective immediately, it's you not me, and please let me know where I can pick up my paycheck for days worked. There's too many jobs out there to bend over backwards for one.