This will show you how to earn the Training Day achievement in StarCraft II on the newest patch, 1.1.2. It's slightly different than before, whereas the Terran Barracks now requires a Supply Depot before it can be built. You can most likely do this faster, as there are a couple of errors here and there, but I scraped in producing the tenth Marine at 4 minutes and 15 seconds - five seconds inside the time limit of 320 seconds (5 minutes 20 seconds) - so it can be done!
Races: Terran v Protoss [Medium AI]
Map: Agria Valley
Time: 5 minutes 15 seconds (it can be done quicker I am sure!)
Make sure the game speed is set to Normal which will make the game run in real time, otherwise you will be on the default 'Faster' setting which will make it a little more difficult to get the achievement due to the increased game tick rate.
The Build Order is as follows:
6/11 Supply Depot - Use the first 50 Minerals towards this
7/19 Refinery - This is used to get the Reactor for the first Barracks
7/19 Barracks - Should be complete by 2:35
10/19 Barracks - Should be complete by 3:55
10/19 Orbital Command
11 through 19/19 Continually Spam Marines - The tenth Marine should be produced at the 5 minute 15 second mark
Once you finish the match, you should be awarded with the Training Day achievement on the match summary screen. This video does not include the award, as I was too lazy to switch over to the NA servers and try it there.
Hope this guide helps!