"Some public relations specialists work a standard 35- to 40-hour week but they often work overtime. Sometimes they must be at work around the clock, especially if there is a crisis. Public relations offices are busy places, work schedules can be irregular. Schedules often have to be rearranged so that workers can deliver speeches, attend meetings and community activities, anc travel."
From the U.S. Department of Labor, Bureau of Labor Statistics Occupational Outlook Handbook