Change date and time of a waypoint in track

Hi all, thats it... I need to change the date and time of the very first waypoint of a track due to I took a short distance from another (and older) track. Why I need do that? Beause Wikiloc takes first and last waypoints to set the overall time; if not track took years...

I can copy a waypoint-track and make a regular waypoint; but not in the opposite way. I tried to copy paste in Word / Excel; respecting the tabs, change date&time, but it doesn't work. I'm using Map Source...

Any idea? Thanks in advance.

Best, 

Carlos Abellanosa