you should train them with your back. Add a couple of back exercises e.g bb bent over rows deadlifts
so your workout will look something like this.
3x8 bb bent over rows
3x8 ez bar curls
3x8 hammer curls
With doin this u will only workout for about 30 mins plus doin your back and thats enough once a week to stimulate them into growth. hope this helps.p.s if u are able to do chins id add 3 sets also as there good for bk and biceps.