About the GPS track log
A typical GPS continuously records tracks (a bread crumb trail) of where you have been. These tracks always include a longitude and latitude, and may also include date/time, elevation, and other information. Consult your GPS manual for details.
Some older GPS receivers discard the date/time information on saved tracks. Several Garmin units including the GPSMAP 76CS, for example, discard date/time information on saved tracks, but keep date/time information as long as you don't save. However, other units, like Garmin ForeTrex 101, do not exhibit this behavior. Test your GPS unit to determine its behavior.