In regards to the time we have in our lives -- like a weight, for one it could be extremely heavy, and for the other it could be sufferable. Thus, like a weight can be both easy and heavy, life can be both long and short; it all depends on what you compare it. If you compare it to doing nothing for 70–100 years, than life is extremely long, but if you compare it to the age of Earth, an average human lifespan is very short. Hence life can be both long and short at the same time, because there are no objective, universal measurements to check whether the average lifespan is long or short, beyond those what we choose to compare it to.
The same thing goes for wasting time or using it efficiently - there are no objective, scientific ways and criteria to measure whether too much time is either wasted or used productively, beyond the criteria we choose or learn to choose. If we choose fun as the criteria, then playing video games every weekend is a life well spent; if we choose strength as the criteria, then having training regime and a disciplined life is a life well spent; if we choose altruism, then contributing to others as much as possible is a life well spent.
Only an individual can choose or be learned to choose to determine this on their own life. This is because each person’s life is their own property by existence, meaning that individual preferences are the best way to choose how and whether is a life well spent, additionally because every individual has their own preferences and thus their own choice of criteria on this issue.
For me, life is not short but very long and full of potential to be actualized.
For me, a life well spent is a life dedicated to intellectual and physical exercises, for they are to maintain and develop the body and the mind. Simply writing this answer validates my confidence in my life being well spent.
Thus, like Nietzsche would probably tell you -- in order to optimally determine on whether or not the time of your life is being well spent, a set of principles in regards to this subject is ought to be created and followed, and with this subjective philosophy you have the opportunity not only to better evaluate your time, but also get closer to your ambitions, as well.