Everything we call "the past" is, literally, nothing but present
memories. Likewise, everything we call "the future" is nothing but
present memories inverted, or rearranged, to form a prediction or
expectation. The appearance of "time" is little more than a trick
of memory, as the Avatamsaka Sutra (Flower Ornament Scripture)
says. You can easily discern this for yourself: simply figure out
what it is you consider "the past" and "the future." You will
discover that it is nothing but thoughts--nothing but memories,
nothing but expectations, nothing but mental commentary. It's "all
in your head," so to speak. There's really no such thing as time.
There is really only Now--an eternally present Present with no
beginning and no ending. Everything is completely new, distinct,
and original every instant, with no real "change" or "motion" at
all. The mystic-philosopher Heraclitus, explaining this point,
said, "A man cannot step in the same river twice."
http://www.buddhistinformation.com/buddhism_and_the_illusion_of_time.htm
This is a very good website on time.