I just want to add some information to the solution by NarrBitaYarr.
You need 30 primary any 50 secondary objectives. Rooftops earns you 2 primary objectives every time, which means, you have to play 15 matches of Stopwatch.
Besides the 2 primary objectives you can get up to 5 secondary objectives. 1 of them is the dynamite mentioned above. You should skip this all the time. If you do the maths, you'll see that you'll get 60 secondarys if you do all 4 every time. So thats 10 too much. You can save some time if you do 4 secondarys in the first 5 matches and then only do 3 in the last ten matches. When you start out, build the machine gun (1st secondary). Then run ahead and plant the dynamite at the sniper-tower (2nd secondary). Run 90° to the right and you can build a protection wall (3rd secondary). Run around the wall and build the bridge (1st primary). Run over the bridge, turn left and run up the slope and turn right again. Run ahead, down the slope and turn left. Run straight and you end up in a wide open area, where you can build another wall (4th secondary). A little bit to the right and straight ahead would be the dynamite which you should avoid, so instead run to the left and straight ahead, till you can enter the generater area to the right. Cross this area and enter the building where you can pick up the intel (2nd primary) Exit the building again and run across the generator area and further straight ahead, till you come to a ladder. Climb it up, enter the building and you can transmit the intel. I'd suggest skipping the first buildable wall after the first 5 matches, since it blocks your path to the bridge when it's built.
I stopwatched a match and with the annoying loading, waiting and warmup times, one 2player-match of 2 rounds (i.e. every one does the objectives once) takes about 8 minutes. Take this times 15 and you end up with 120 minutes. Add meeting and loading times to that and you'll see, that you need a 2 and 1/2 hour session for this achievement. It took each of us only about 75 to 80 seconds to finish a round. So you see, that you spend more time waiting than playing when you do this.
Edit: to profit from "Quick hands" you have to activate your veil-speed while building, which uses up energy, you could also use for running faster. So I don't know, if it's worth trading in running speed for faster building. I guess it won't make any difference timewise.