Timestamp for triggered events

Hi, thanks for the hugely useful documentation/website. I've been able to answer most of my questions. Nevertheless I need your advice on the following application. I've to capture events on two digital outputs of a device. Events on the first output occur with a frequency which is approximately 8 Hz, on the secend output events occur with a freqency which is approximately 20 Hz. I'd like use a digital input line of the U6 to detect the occurrence of an event on each of the outputs of my device and tag them with an accurate timestamp. To be exact i need a timestamp with an accurancy of less or equal than one millisecond. Since I'm not running a real time OS, using timesamps of my system is not an option. So I need help to find a way, to use the U6 internal system timer to generate timestamps when events occur on the two digital input lines. Thanks in advance! Jan