I have worked rotating shifts for the last 20 or so years at a number of facilities. There are as many schedules out there as there are people. The most important thing to think about before deciding on a schedule is what type of work the 2 men will be doing. Can they swap roles, or is there certification or union constrictions as to their duties on shift. If they can swap duties, a four-crew system is possible, however you will require a relief position for vacation & sick time. A four-crew system usually involves scheduled overtime, which is costly. The chosen schedule is usually a repeating rotating set of dayshifts and nightshifts, over a multiple of four weeks long(i.e. 8 weeks x 42 hours/week = 336 hours). A normal four-crew system has great advantages when the crew is large (6+ people) that can all swap jobs, and an extra man over normal requirements is assigned to the crew. The crew becomes autonomous, scheduling vacation, dealing with sick time off, emergency time off, training, etc. by themselves, without costing overtime.
If your operators cannot swap roles, or the crew is small, such as yours, normally a 5-crew system is more practical and less expensive. There are 6 and 7 crew systems as well (another discussion). With a five-crew system the chosen schedule is a multiple of 5 weeks long. The operators are scheduled to an average of 40 hours/week. This leaves four crews operating on any one day, and one crew on spare shift. The spare shifts are used for vacation, sick time, training, etc. There are usually a bunch of rules for management to deal with, but, are usually for a small crew are not that bad (i.e. who gets first choice on holidays, Christmas off, etc.).
Location usually plays a role in what type of rotation you choose. If your plant is in a remote location, a longer stretch working for a longer stretch off is usually the norm. If the plant is near recreation, a rotation involving shorter shifts on/off could work well. Rotating from nightshift to dayshift every set is what is most prevalent in industry. The operators on extended nightshift loose touch with the operation, and their families. This is a major stress factor, and contributes to overall poor mental health. Physically, it would be best to remain on nightshift forever, if you didn't swap back to dayshift on your days off work (which is not likely).
Finally, I would recommend that you let the crews choose the actual schedule as they are the ones working it. If you set the boundaries (five crew, four crew/no more than four shifts in a row etc.), and give it a try for at least 2 rotations, and then vote on continuing, or choose a new schedule.
Operators value their schedule highly and choose their place of employment based on how it functions.
I hope this helps, there are a number of companies out there in business to just optimize shift schedules.
I can email you a few schedules I have collected over the years if you send me your address, I'll pass them along in excel format
shyst