WatchInterval is a Cardinal property used to determine the time, in milliseconds, between execution of the event-based timer used by TIdIPWatch. The default value for WatchInterval is IP_WATCH_INTERVAL. 

WatchInterval is used at runtime when the value in Active changes from False to True. The associated event-based timer in the internal TIdIPWatchThread instance is created, initialized to use the value in WatchInterval, and the thread is started. If the value in WatchInterval is changed after Active set to True, the Interval property for the internal TIdIPWatchThread instance is updated to contain the same value.

(Delphi) Changing the interval and event handler for the thread timer event in TIdIPWatch. 

   IdIPWatch1.WatchInterval := 15000;  // 15 seconds
   IdIPWatch1.OnStatusChanged := UIShowStatusChange;
   IDIPWatch1.Active := True;

TIdIPWatchThread Active OnStatusChanged