I live 3.5 hours from Atlanta Airport, I am driving and also need to park my vehicle and get to security, then gate.  How much time should?

use your 3.5 hours commute time, then add 2-3 hours on to it for the airport process 

Six hours or so, depending on the time of day.  As others have noted.  You want to be inside the airport terminal two hours prior to your flight.  Hartsfield is big and security lines could be long. 

It could take you 10-15 minutes to find a place to park.  If you choose an off-airport parking facility, you need to add in the time for the shuttle to take you to the terminal. 

If you plan to grab a meal before getting on the plane,  you should have time if you arrive two hours in advance of your flight.  

You should be IN the airport at least 2 hours before a domestic flight departure time, and even a bit earlier for an international flight.  So I would leave at least 6-7 hours ahead of departure to allow for traffic, parking, and transit from parking to the terminal.

Leave 5.5 to 6 hours before departure.

Plan for traffic delays.

Plan to be at the airport and looking for the parking garage not less than 2 1/2 hours before your flight. Three hours would be better.

You need to be at the airline's check-in counter and standing in line not less than two (2) full hour before your flight is scheduled to depart. Make it three hours if it is an international trip. 

Consider driving to ATL the day before and spending the night in an airport hotel. Especially if making your flight is critical. 

You live 3.5 hours away with normal traffic. The day you need to go plan on it not being normal.

You are to be at the check in area about 2 hours (domestic) before a flight. NOT WANDERING the parking lots looking for a spot.

As you are new to Airport and navigating where you need to go Allow two hours to get from parking space to the terminal

You are leaving home about 8-9 hours before flight. Allow a few minutes for a pit stop along the way. A stop just before you get to Atlanta.

You might want to consider travelling the day before and sleeping near the Airport and using the Hotel shuttle Depends on the time of day of your departure..

NO NEED to do the express dash and be frantic as you rush around the Airport doing what you need to do.

2 hours, especially if you're going to park at one of the cheaper, outer lots and take the shuttle bus in. The Atlanta airport is the busiest airport in the US. If you're checking a bag, you wait in one line to check it, then a LONG line to go through security. After that, you ride a train to your terminal.

You want to have at least an hour extra minimum, 2 hours is even better, it is better to wait at the gate a bit then to miss your flight. 2 hours for a domestic flight, 3 hours for an international, that's just a general guideline.

You have to consider traffic. What time will you be driving there, what kind of traffic is usual for that time, also you want to give spare time in case of a slowdown because of an accident or something.

Also consider that on holidays it will get a lot slower, because obviously a lot more people are traveling during those days.

Parking will take a bit of time too, and getting to the terminals from there will take some time.

You'll have to go through security checkpoint, that takes time, could be quick like 10 minutes, could be longer and if you have baggage that will take a lot more time.

If you don't have any baggage, just carry on, it will be faster and 2 extra hours should be more than enough to get through all the things and get to your gate.

Flying somewhere takes the whole day away anyway so it is better to be there early and wait then to be in a rush the whole time worrying about if you will make it or not.

1-2 hours before departing