Hi
For about 4 weeks I have been using my arm bike for between 35 and 51 minutes per day almost daily. My schedule is going to change next week.
Is it as effective to do half the workout in the am (my preferable time) and half at night?
I have to get at least 6.5 hours of sleep per night and to do the full and still get out on time I'd only be able to get 6. I've tried to go to bed earlier it just doesnt happen.

I've heard conflicting advice on this. The rule used to be you had to do all your workout at once or else don't bother. The general view now is that the aggregate of all your exercise for the day should equal the same amount of time. I'm not sure how this would transfer to an arm bike that is used for toning vs cardio. I would do what you can, splitting the routine into two sets for a week or two and see if you get the same results as the one long set and if not, try a new tactic.

If I have to split up my workout, I always make sure I work a lot harder at both. So where I run usually jog four miles altogether most nights. If I had to split it up, I would alternate running and jogging. I would run one lap and jog two, run one, jog two. Do two miles of that. Then later, I would do the same thing for another two miles.

I wouldn't worry about, it is actually great to do exercise twice a day. Just give it full effort for both sessions and you'll be doing great!

For me the Arm bike is actually cardio I average 11/12 mph I figure if I split it I'll do 4 in the morning and 4 at night