If your goal is to burn the most fat in the least amount of time then stop spending so much time on these 5 exercises.

1) The bicep curl
2) The tricep extension
3) Seated leg extension
4) The assisted crunch (on machine)
5) The abductor or the adductor for legs (on machine)

Here's why they arent very helpful:

First of all rather than dividing your workouts up into body parts (legs today, triceps tomorrow, shoulders the day after) focus on the whole body each time you exercise. This is safe if you're just trying to lose weight and "tone up". If you happen to be in too much pain, go easy or skip the day. With total body you're getting more bang for your buck.
Often I see gym members standing around bicep curling all day and pausing and sitting in between sets for 30 seconds or so. This won't get you what you're looking for in your physique. For weight loss you've got to constantly move and focus on movements that work more muscle groups at once. For example the seated row, the bent over row and the standing row work the arms and back. All rows lead to great arms and more calories burned. Other exercises that work alot at once are the squat, the lunge and the over head press and the pushup.

So unless you are mixing in these 5 exercises with other exercises I'd skip them.