Mate, triceps are a reletively small muscle and don't require a great deal of stimulus to get them pumped. They also don't require a huge volume of work because they assist in so many other exercises. Just choose 2 of those exercises you currently use. With good form and the correct weight 3 sets of 8-10 each should be plenty.
3 hrs is a very long time to spend in a gym. Remember, more is not necessarily better in regards to
weight training. Overtraining is very detrimental to muscle growth. The body goes into a
catabolic state ie opposite to what we actually want to happen. Gooseneck has suggested the optimal time frame. As long as you train intensely and smart, this should be more than adequate.