endorphin rush, when does it go away?

If I go out and hammer a road ride for an hour or a cyclocross race I can have a pretty good endrophin buzz. Good enough to go out and do another cross race and still be feeling good but my legs might get toasted. I did an 80 mile half gravel ride on the corss bike with the gang a while back. Steep climbs on the gravel. Steeper than the paved roads. In any event any endophins I had floating about were consumed by then end of that ride. So I ask, when does that endophin buzz get consumed. Maybe I will go off to internet research to see if anyone has tried to answer that.