When going through Apache 2.2 access logs, logging with the %D directive (The time taken to serve the request, in microseconds), that it's very common for a 200 response to have a given number of bytes, but a "time to serve" of zero.

For example, a given URL might be requested 10 times in a single day, and a 200 response is sent for them all, and all return, say 1000 bytes. However, 7 of them have a "time to serve" of zero, while the other 3 have a time to serve of 1 second.

Is this simply because the request was served faster than the resolution of the timer Apache uses?