MS Project does have a default 24-hour calendar included when you install, but it is not selected by default. I recommend setting your project calendar to the 24/7 calendar. That will help with the tasks that have no resources assigned.

You also should create special calendars for your various shifts. Often I see drilling operations with unusual shifts, particularly offshore drilling. People may be out on the rig for several weeks at a time, working seven days per week for an eight-hour or even 12-hour shift every day. Other drilling operations are run with three eight-hour shifts working five days a week, with some sort of overlap or special shift to cover the remaining two days per week.

Write down your shift patterns and the single-employee exceptions. Figure out how many calendars to create, to help maintain the work properly. You will need at least two calendars (if you do two 12-hour shifts), but you might need many more to cover the various days of the week and times of day that people come off and on shift. The “night shift” calendar included in MS Project will give you a model to start with.

Once you have your calendars defined, you can set up your resources, and assign the correct calendar to each resource. Then make individual exceptions as needed for each resource.

MS Project can help for scheduling this type of work, because it will track when each resource is on and off shift. If you assign two people to the same task from two different shifts, you will see strange effects because they never work the same hours. Watch your calendars carefully, and the tool should help you a lot.

Also, if you want to simplify your MS Project administration work, you can ignore the shift issues entirely. Just create general resources like “engineer” or “laborer” and assign them all to a 24-hour calendar. Of course, this sacrifices the ability to see who is doing what when, but it makes administration of the schedule simpler.

Best of luck!