Most NI DAQ devices do not keep a record of that information, so you would need to know exactly which model you were referring to, and someone would have to dig into the specifications to see if it was possible with that device.
Instead you would generally keep track at the MATLAB level of the time you asked the device to start recording, and then at any point compute the elapsed time.
If you are using the newer version of the NIDAQ interface that automatically includes timestamps with the recorded information, then you would typically look at the very first timestamp associated with the data you logged, and subtract that from all of the other time stamps to get the elapsed time since that event. Which is not exactly the same thing as the elapsed time from the beginning of when the device was asked to start recording (since an unknown amount of time elapses between the time a device is asked to start recording and when it has the first data ready -- especially if you have a trigger condition set.)
