The entire game is built around learning the door code. If you know the door code in advance, then the only item you need to beat the game is the chair leg (to get the pencil and the glass shard).
Having to get 5:30 minutes or less on every level leaves the difficulty a little erratic. Some levels can be comfortably breezed through, while others force you to fight tooth-and-nail for every last second due to too much ground to cover or too many enemies. Scaling the times based on the level's size might save a few headaches. Very enjoyable otherwise.
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