Stomp kill: 0.8s
Kill: 0.3s
One-shot-kill: .5s
Headshot kill: .5s
Impale kill: .8s
Explosion kill: 1.0s
Chain kill (x2): 2.0s
Bear trap kill: 1.0s
Swarm kill: 1.0s
For the wave based levels, these values multiplied by 100 are the number of points you gain.

• Generally if your time is close to the cutoff, that means you are missing an opportunity to kill enemies in unique ways. Explosive kills are king in terms of speed vs amount of time gained.
  
• Bear traps can be thrown and act similar to throwing knives.
  
• If there is a rocket launcher that you're not using, or an explosive barrel that isn't being shot, there's time being left on the table. In most cases there are significant numbers of enemies that can be bypassed with just a few explosive barrels.
  
• Analyzing the context can help you find better ways to kill enemies. If they're running at you in a line, try to get a collateral with the sniper rifle. If there is a laser trap, shoot that to blow them up for an explosive kill.
  
• The plant health items have a delayed heal, the medical kits heal you instantly. On some of the later levels it is essential to pick up almost every health item.

Final and most important tip is to mutter "beast mode" under your breath while playing.