If your primary goal is to build your arms you need to let them rest more.
If you perform your triceps workouts during your chest workouts you will not be
able to devote all the possible energy from your triceps.
If you are trained and have been working out regularly, and want to build
your arms, perform biceps exercises while they are fresh, i.e. during your chest
Devoting a day to arms only is a must if you really want to build your arms.
Try to superset biceps & triceps exercises to pump your arms muscles to the max.
Here's an example of using your same days off
Day5: Arms (Triceps/biceps)
It would be better to workout with a 2-3 on 1 off training split for your
Here would be a very good training split for your goals
Day6: Arms (biceps/triceps)
Remember, it is your diet which will determine whether you actually build