What I can suggest in your case is the following:
1) Use the setTimeout method as already suggested with the desired show delay value
2) Attach a handler to onmouseout event of the target control and set some flag there
3) Handle the tooltip's OnClientBeforeShow event and check the flag from 2) there; if it is set, the mouse has left the target and you can cancel the show by using the args.set_cancel(true) syntax; clear the flag;
I hope that my suggestion is helpful, let me know how it goes.
the Telerik team