"Now" depends on the frequency. Light vibrates at frequencies far beyond the time-scale of our consciousness, so we perceive visual events as occurring more-or-less "instantaneously."
Perception of sound, however, is spread out over time. We do not perceive the instantaneous sound pressure; rather, we perceive the frequency of the sound-pressure variation. Frequency is a concept which has no "instantaneous" meaning. Thus, in order to "hear" a tone, the past, the present, and the anticipated future are melded together in our consciousness.
Appreciating music stretches our perception of the "present" even further. To perceive a tone, our "awareness" of the vibration must be over a period on a time-scale of milliseconds. To perceive a melody, our "awareness" of the notes must be over a period on a time-scale of seconds. And to really appreciate a 12-bar blues progression (or jazz especially), our "awareness" of the melodic and harmonic relationship between notes must be on a time-scale of minutes!
Thus, the idea that we are "conscious" of just one instantaneous slice of time is just plain wrong. How could we perceive motion at all without constantly comparing an object's present position with its position in the recent past?
Therefore, we are not conscious of "now" and "now" alone. Our consciousness is "spread out" in time, with no definite time-scale to the spread out-ness. At the lower limit, we can perceive changes in the world taking place over millisecond time-scales. The upper limit seems bounded only by our attention span.