As I explained in your previous question about this:
1. You need to initialise the $SeenClock story variable at the start of your story, and you do that within a startup tagged special passage.
Add a new Passage to your project, I name mine Startup but you can name it whatever you like because the name isn't important. Assign this new passage a startup Passage Tag, and then copy the following into that passage's body.
(set: $SeenClock to false)
2. In the passage you want to conditionally see the link in add the following code, it first checks the current value of the $SeenClock story variable and if it's equal to false then it will show the link to the Look at the clock passage.
(if: not $SeenClock)[
[[Look at the clock]]
3. Create a new Passage named Look at the clock and place the following code in it, you will also want to add some text decribing the character looking at the clock.
(set: $SeenClock to true)