this achievement is actually really easy. things you will need to have done will be have played upto the 1st nyc hideout level.
ok heres what you do load game, mission, easy, NYC - JBA HQ - Part 1
follow jamie to the bedroom, then follow moss to the assault course a timer will start for 25 mins go make a sandwich or get a drink what ever floats your boat.
make sure if you have a wireless pad to nudge it after 15 mins or it will turn off.
after 25 mins moss will come back he will be mad that you did do the assault course but follow him downstairs to the other room and then shoot the helicopter piolt to regain some trust you lost from not doing the assault course you will get a small cut scene and then after that your achievement will unlock. HAPPY DAYS.