What cut is it? A roast of beef could be anything from tenderloin or rib-eye to a lump of sirloin, rump or anything. 'Roast' tells little more than that is a lump of meat.
You're working on 10-12 hour cook... hmmm... that could be a standing rib roast. If so, it really doesn't need much more than time to come up to temperature. If it is a bone in roast you could remove the bone to speed the cooking process.
Depending on the cut, an extra 8 hours cooking time won't make a detrimental amount of difference to the outcome. You could potentially put it in to cook before retiring. But, as you don't tell us the cut it is difficult to know.
Another option is dividing the roast as suggested earlier. This would abbreviate the cook some.
I'v noticed that people seem to plant the menu and then try to avoid the requirements for cooking it. A more sensible option would be to select the menu according to the cooking time you have available. Work your time backwards and then select a cut that will enjoy an 18 -24 hour bath time. This would allow you to relax and enjoy the cooking process.