Time 4 is used when you want a timed trigger on a spell effect. Specifically,
Trigger Effect: Allows the mage to generate a keyed pause: Something
that doesn't happen until a specific person, creature, or item comes
into the right position.
Mage: The Ascension 20th Anniversary Edition, Pg 523
Notice how it says a specific person, creature, or item. So in your second example, if you only wanted the rune to affect a specific person walking by and not all people, you could use Time 4 to do that.
Otherwise, the effect you're creating takes effect when you finish casting it based on how you describe what you want it to do and what powers it uses.
For example, if you're creating a poison using the well known rote Persephone's Nectar (Correspondence 3, Life 3, Matter 2), it turns an ordinary liquid into a poison and only affects the given target when they imbibe the poison.
If you wanted to have an effect triggered by some event you would need not to use Time 4 (Trigger Effect) but simply state the effect as being "when someone looks upon this rune, they become confused to the point of insanity." Whether it's Vulgar or not is up to your Storyteller (more than likely it is, though if they're confused to the point of insanity it may not count, depending on your worldview).
Here's an example of a "triggered" effect that doesn't use the Trigger Effect power of Time 4:
Receptacle for lesser forces (Forces 2 Prime 2)
The mage consecrates a container (like a flask, a box, or a statue) to be able to contain forces, fills it with force, and then seals it. When the seal is broken (or the spell fades) the forces will be set free...
Note that the "trigger" is simply breaking the seal on the container, and this rote does not use Time 4.