It is always a better morning when you find your own bugs 
The different total times I was getting was caused by additional clicks registered inside some iterations of animation_mouse.time.
So, instead of using
I just get the first value in the array
rts.append(animation_mouse.time[0])
Now, I don’t even have to flat lists anymore 
I’m not used to Builder so I’m still learning how to debug using it.
I would like to thank @Becca and @wakecarter for all the great contributions to this forum.
They are helping me a lot
I hope this, at list, helps someone else.
Best,
Flavio