By the third day, you should definitely see some bubbling and, if not, let it go a bit longer; depending on how warm your house is and how active your starter, you may need to begin feeding more often, or even move to two feedings a day roughly 12 hours apart, like in the morning and at night.
In a nutshell, you want to feed the starter only after it has peaked (metabolized all the flour from the last feeding) and has started sinking down or gets liquidy- this is when it is hungry; this might be 12 hours, it might be 14, it might be 18, or 24, depending on the temperature in your house. In very warm climates it may only be 8 hours.
It is better to underfeed rather than overfeed here; for each feeding, like before, discard all but 1/2 cup of the starter (keeping roughly ½-cup of starter in the jar (~ 4 ounces).
Add 1 cup bread flour, spooned and leveled, and 1/2 cup water to the 1/2 cup starter and let this rest at room temperature for 12 - 24 hours or until the starter looks “hungry” again before repeating.