There are two possible issues that come into play and that may be why you are asking that question.
1. When one first starts comprehending Buddha Dhamma at a deeper level, one becomes a Sotapanna Anugami. That means one gets into the path (magga).
– But it may take many days or even many years for a Sotapanna Anugami to cultivate that path and to become a Sotapanna.
2. There is another event that happens at the moment a Sotapanna Anugami becomes a Sotapanna. At the moment, a citta vithi (series of citta) flows and there are three cittas that arise towards the end of that citta vithi. One is the magga citta. That citta is followed by two phala cittas and that is the exact moment that one becomes a Sotapanna.
– This magga citta is different from following the path (magga) as a Sotapanna Anugami in #1 above.
So, it could take even years for a Sotapanna Anugami to get to the Sotapanna phala moment (i.e., to become a Sotapanna).
– But there is essentially no time gap between a magga citta and phala citta.
Please feel free to ask questions if the above explanation is not clear.