Here is a guide I just wrote up for others that might read this... this a compilation of methods I learned/worked out with Famine and Druton from GTAF...
Just thought I'd share this for those going for the times for Fly the Co-op trophy/achievement...
I know one of the biggest pains for doing this is getting the bikers to spawn in the boat while doing 2 player-- while this makes it easier, it does not make it impossible to get the time. I know some people know this stuff but I've yet to see a good guide showing this... other then 007crafts youtube video-- which only allows for the boat spawn.
For game setting I use the following--
-2 Player
-Time of day- midday
-Weather-clear
-Reticule health-on (so you know you've killed someone)
-Traffic- Parked (will speed up the drive-- see below)
I've done this mission alot the last few weeks, first getting my trophy and then doing it with others to get their trophies.
I have managed to get the time on 2 of the 3 land spawn locations (without mics or headsets), based on the speed of runs I've done and how fast I've cut off the fleeing the bikers the 3rd is possible too... the key is to:
1. Clear the building fast
2. Have a good heli pilot who knows where to land to cut them off (in front of the bikers)...
For #1, I've managed to speed this up a bit by having one of the players drive, while the other flies... it is possible to drive to the location faster then you can fly there... you just have to get on the highway fast and then drive off the highway where there is a gap in the rail.. The driver (if good) will arrive about 10-15 seconds faster then the flier.
To get on the highway follow this route
Get on highway fast
Then drive off the highway at this spot
Drive off highway
You can either brake and make a hard right, drive off and on top of the warehouse there, drive over it and off the building to the Southwest or you can just drive it straight off a full throttle you will land near the bend of the road and then it is a straight shot west to the deal breaker building
Having someone drive and the other fly does 2 things, it seems to make more bikers spawn on the ground level (when the driver arrives first) and these are easier to clear IMO then inside the building... it doesn't take a whole lot more time to sweep the upper levels with one player then with two as there are always just 7 bad guys on the 5th level and above and they are always in the same places.
The flier clears the building down from the top-- there are 4 bad guys up top, I always go down on the east side as there is a guy with a shotgun near the stairs on the SW side on the 6th level. Clear the 3 guys on the 6th. Nobody on the 5th (but there is a rocket launcher near the stairs on the east side you might want to grab. The majority of the bad guys the flier will encounter are on the 4th and 3rd level.
As the driver I usually will work around the N. side of the building, getting everyone on the N. side (there will be quite a few) including all the bad guys you can reach on the 2nd floor from the ground then work up to the 3rd level sweeping each level to collect each card dropped-- you should encounter your partner on either the 3rd or 4th floor and be clearing up any stragglers/cards. To have a shot at the time, you have to have the building cleared before the 5 minute point-- the faster the better.
The driver is responsible for getting the boat. If you get the boat spawn and are on the 4th floor or higher, just jump off on the W. side-- you will die but you do keep your rocket launcher... then just run to the pier and kill them-- you can kill them with the AK-47 if you don't have the rocket launcher, without the rocket launcher it is easiest if you kill the boat driver first.
The Flyer is meanwhile grabbing the heli and picking up the driver (just like 007crafts video).
If you get the land spawn, both the driver and flier should head to the roof. The pilot should get in and as the blades spin up, quickly check the maps to see where the bikers spawned... 3 possible locations (the spawn locations are approximate in my maps), then fly to the appropriate cut off point immediately, be careful not to fly directly over the bikers as it will make them drive faster.
Spawn Location #1
In the above, the spawn location is near the dot on the left, the cut off point is on the right-- you will land in the street just east of the police station there... kill the bikers as they make the turn to your south... rocket launcher is best for the van, rifles for bikes IMO...
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Spawn Location #2
In the above, the bikers will spawn near the right dot, drive up the ramp up onto the highway ... just land on the highway in front of them and wait..
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Spawn Location #3
In the above, the bikers will spawn near the lower dot, fly to the upper dot and land.
I've only done this on PS3.... so cannot verify the above will work on other platforms...
Once again, it is important to not fly over the bikers when flying to the cut off points as it will only make them drive faster.
Hope this helps someone-- I would not expect this guide to help you instantly pass the mission, it takes practice learning how to clear the building fast and as you know, anything can go wrong with these missions.
Thanks to Famine (at gtplanet.net) for helping me work out the driving/flying thing and to Druton (at GTAForums.com) for being such a great heli pilot (I used to think I was pretty good) and showing me how you can cut off the fleeing bikers relatively fast-- I've varied slightly from his cutoff points to save a bit more time