My 2 cents.
It sounds like you are into lighter weights for maximum number of repetitions, i see you are 24, appear to be familiar with the importance of good nutrition (protein, carbs, fat, etc) and sleeping habits.
With all that said (and assuming your are trying to tone not bulk up) i would suggest a workout lasting no more than 45 minutes at a time, 5-6 days a week, no more than two muscle groups at a time, and working the same body parts every 5-7 days. For example, Back + triceps / Chest + biceps / Legs + shoulders.
Another approach (the one i actually use)is as follows: Day 1 - muscle workut, Day 2 - muscle workout, Day 3 Cardio, Day 4 muscles workout, Day 5 Cardio, Day Six - day off, Day 7 (this is actually back to day 1). Using this method i workout the same body part every 6 days - the general recommendation is every 5-7 days. I never try to go more than 7 days without working the same body part. Anything beyond 10 days and i loose strength.
You may have to play around with what works for you and your schedule.
Forgot to mention - changing your muscle groups/routine is very important to stimulate new growth and keep you motivated. This includes the specific exercise you are doing. For example, if you have been doing bicep curls with a dumbell for a while try changing to a bar for biceps curl and so on for the other muscle groups. I would encourage you to do this every two months. Also, free weights are better than machines for adding bulk. - my take on things.