Seemd like the time is often incorrect on hotel alarm clocks and there is no way to set the time. Also, most have battery backups so unplugging them may not do any good. I never set the alarm, relying on my mobile phone's built in alarm.
Ok... Occasionally, I set the clock if I have to get up very early and the people next door have kept me awake with a loud TV or partying. Then, I might set the alarm to a local radio station, preferably RAP, and crank the volume WAY up and program it to go off a couple minutes after I leave the room.