Depending on the size of the playerbase, you'll want to keep a fair medium of staff available for players. I'd say 1 immortal per 10 players or so. Then they can take care of concerns in a manner that will seem less like a job on the busy days, and give them opportunity to create storylines and quests on the slow days.
You can also give people certain tasks to take care of, which not only takes some of the burden off your own shoulders, but also gives them a goal to work for, and not have to worry about several other things at the same time.
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