Using ScheduledTasks can accomplish this... here is just one example (with 10 seconds so you don't have to wait too long to see it work):
Module[{nb},
nb = CreateDialog[Style["Initilization complete"]];
RunScheduledTask[NotebookClose[nb], {1}, AbsoluteTime[Date[] + {0, 0, 0, 0, 0, 10}]]
]
