It will only show breadcrumbs for the last few hours but it will store all of the data in the TCX file. Don't reset the timer, there is no point.
Really? Are you sure? According to Garmin, if you don't reset the timer, it will overwrite the history from the first 4 hours with the next 4 hours.
You've got yours set to every second and it actually saves the data (altitude, gradient, speed, power, etc) from a 6 hour ride without resetting the timer?