First things you should do is prep your boat so that you are ready to launch when it is your turn at the ramp. You don't want to be "that guy" wasting everyone's time who is behind you ready to launch. This means before you get in line, pull off to the staging area and take off your transom straps, transom saver, and most importantly make sure your plug is in. This is also the time to load anything else you may want to bring on the boat such as fishing gear and coolers. You do not take off your bow strap at this step, keep it attached until the motor is in the water and you are about to back it off of the trailer.
Once your boat is prepped and ready to rock, go ahead and get in line. If no one is ahead of you, make your way to an open lane and line yourself up. Make sure you do this without cutting in front of someone, thats how many confrontations start.
When you are lined up to a free lane, back your boat up parallel to the dock until the top of your trailer fenders are just barely out of the water. This technique is a good rule of thumb, although all boat launches are different. When it comes time for loading your boat onto the trailer, have the trailer submerged at the same depth. Nine times out of ten that is the perfect hight for the hull of the boat to sit nicely on the bunks. Also, make your truck window is down and the radio is off so that the driver and captain can communicate with each other.
At this point the driver should get out and unhook the bow strap and safety chain. The captain of the boat should tilt the motor down into the water and start it up. Remember you still have people behind you waiting so don't sit there longer than you need to. Once the motor is running, put the boat into reverse and back off of the trailer.
After the boat is in the water, the driver can pull the trailer out and park the truck in the parking lot. The person in the boat should back away from the launch and idle at a save distance out of other boaters way. Once the other passenger has made it back to the dock or shore, make your way to pick them up. Remember that you still have to wait your turn to pick them up at an open spot.
The process from actually putting the boat and trailer in the water, getting the boat off, and pulling the trailer out should not take any more than a few minutes. Five would kind of be on the long side though. If you follow these rules of the ramp you shouldn't have any problem doing it in that time frame. Obviously the best way to get this process down is to practice and get familiar with your boat and the depth your trailer should be. If you are trying to get out on the lake this weekend and you are fairly new to boating, my suggestion is to get out there early before the rush. Hopefully it wont be as busy and you wont feel as rushed.
Also remember that safety should be your number one concern out on the water!