Time is not a continuum; every moment is special, every moment has a special task for which it is uniquely suited; every moment is a now that has never existed before and will never exist again, because tomorrow and the next day have their own opportunities and challenges. One must be sensitive to the call of the particular hour.  And if not now, when?  (Avos 1:14)  If I do not seize the opportunity now and imbue the moment with its particular meaning, the opportunity might not be there when I am ready ~ Chiddushei HaRim as quoted in The Pirkei Avos Treasury