Contra

When you are in the tunnel, just progress about half way through, or right near the end, and just wait until the time runs out. You will then die and respawn in the same location with a full set of time. Then just leave and you should have well over 33 seconds to spare. Do the same for the other.

You must beat the first timed tunnel with 33 seconds to spare. I recommend using the rapid fire gun. It can deal out a lot of damage real quick to the flashing lights you need to destroy.

This can be done without dying. I found that the rapid fire gun is most effective, although the spray works too. There's no real time to waste, I had exactly 33 seconds left both times I did this.

The trick is not to get caught up destroying everything in sight. There is only one target to hit, the rest of what is shooting at you is a distraction. Simply duck when fired upon and shoot for the target. Ignore everything else (except don't get killed). Also, keep an eye on the map, going the wrong direction will lead you into trying to walk through a wall and will take away precious time.

Definatly recommend the laser for this. It's incredibly easy to hit the targets with it and they only require one shot to explode. Don't bother with all the enemies and other turrets in the walls, just focus on the tiny light that becomes exposed just after the turrets open up. You don't need to die and you can easily complete the tunnel with 40+ seconds remaining.