Please use the Question Tags to state the name and full version number of the Story Format you are using, instead of including that within the actual Question itself. It makes it easier for the Answer to see and easier for Others to search for.
You can use Hidden hook markup to hide the relevant text, a (show:) macro to reveal that named text later, and a (live:) macro to cause the delay. You will also need to use a (stop:) macro to stop the timer that is created by the (live:) macro.
Wait three seconds and a clue will appear.
|clue)[This text was hidden when the passage is first shown.]
note: The above also used Collapsing white-space markup to hide any visual output of the (live:) macro itself, this isn't actually necessary for the above technique to work but it does make it visually cleaner.