A few tips:

• You can fly indefinetely by continuously flinging yourself in mid-air (as shown in the video)
  
• Restarting a stage resets the time consumed in that stage, so if you're on stage 3 and you have 30 seconds on the timer and you spent 10 seconds in that stage, you can restart the stage and get those 10 seconds back, bringing the time down to 20 seconds.
  
• Loading screens do not count in the timer, each loading screen takes about 3 seconds.

Hopefully this guide helped you at least get an idea on how to earn this achievement.
Leave a comment if you come across another technique that could be used.