To get this achievement you need to complete the game in under one hour. It's best to do this on Easy Mode if you're not very good. I cannot remember my exact time on every boss but I remember that when I got to Wily's Fortress I had just over 30 minutes. So that should explain how much time you should use. Make sure you have plenty of E, W, and M Tanks because dying can mean the difference between beating the game in 58 minutes and beating the game in 1 hour and 1 minute (also if you don't die you will get the Invincible Achievement). Also use Beat Calls and Shock Guards. Each Wily Stage should take at most 4 and a half minutes. Use some time saving techniques such as boss weaknesses and I found that it shaves off almost a minute on Wily Stage 3 to use Triple Blade to hit the Block Devil while it is under the stage (the blades go through the floor). I finished with 55 minutes 30 seconds or so. Don't be afraid to try this achievement after a few completed games. The more familiar with the stages you are, the easier it will be to get this.