I need to time some data from some sensors right now I am getting data time resolution down to 1 second, but i need it down to millisecond possibly microsecond resolution. I know that in the time library you can get resolution down to 1 second. I have the adafruit sd card shield with an rtc. I think you would have to use the micros and millis but i don't know how i could get it at the start of the second.
adafruit sd card shield with an rtc