Ich darf mal kurz die Delphi-hilfe zitieren (achtung english!)

Code: 
Sleep 
Unit: IdGlobal
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Suspends the current thread for the specified number of milliseconds.


procedure Sleep(ATime: cardinal);

Parameters

ATime: cardinal

The number of milliseconds to sleep.


Description

Sleep is a procedure used to suspend the current thread of execution
for the number of milliseconds specified in ATime. 
While the current thread is suspended, control passes to other 
processes with an equal or higher priority.
Sleep encapsulates the platform-specific procedures or functions used 
to suspend the current thread of execution. For the Windows platform,
 the procedure used is Windows.Sleep. On the Linux platform, Sleep 
tries to select a non-existent socket handle for the specified number 
of milliseconds.