This is the 272nd most frequent Russian word.
пор
"Пор" in Russian is not a standalone word; it may be a root or prefix, or a truncation. If you mean "пора," it means "time" or "it's time."
In this sentence, "пор" is part of the phrase "с того пор," which specifies a starting point in time, meaning 'since that time'.
С того пор, как мы встретились, мы стали хорошими друзьями.
Since the time we met, we became good friends.
Here, "пор" is used in the expression "до сих пор," which translates to 'until now'.
До сих пор я не могу решить эту задачу.
Until now, I cannot solve this problem.
In this context, "пор" is part of the phrase "с ранних пор," indicating a start of interest from 'early times'.