That's really up to your risk tolerance. The 3 hour suggestion is there to mitigate risks around traffic, parking, security lines, lines for checking bags, etc. How close to cut it is really up to you and your risk tolerance. Being there 3 hours early doesn't hurt anything. You can also be one of those people who get there 4 or 5 hours early. If you get there at the T-90 minute mark, that's ok too as long as you think you can make it through bag-check (if you have checked bags), security, etc. in time and are willing to accept the consequences if something goes wrong.