os.setAlarm

Function os.setAlarm
Adds an alarm which will fire an "alarm" event at the specified Minecraft world time. The returned table acts as a unique ID for the alarm.
Syntax	os.setAlarm(number time)
Returns	table alarmID
Part of	ComputerCraft
API	OS

Explanation

(Forum Post by jag_e_nummer_ett:)

   --(( Basic format ))--
   os.setAlarm(time)
   --(( Will timeout when it's 18 o'clock in the world ))--
   os.setAlarm(18.00)
   --(( Will timeout 2 (in-game) hours later ))--
   os.setAlarm(os.time()+2)
   --(( Basic event layout ))--
   local ev,p1 = os.pullEvent("alarm")
   --(( Event output ))--
   Name: alarm
   Parameter 1: A table that acts like it's unique ID

Example

(Forum Post by MysticT):

   local alarm = os.setAlarm(5)
   while true do
       local evt, arg = os.pullEvent("alarm")
       if arg == alarm then
           print("It's 5:00, wake up!")
       end
   end