Answer:
My days are numbered.
I never was but always will be. No one ever saw me but everyone knows I exist. I give people the motivation to better themselves every day. What am I?
Physicists have built devices to move me very fast. My last seven letters can be commonly found in newspapers magazines and journals.
When the clock has no angle, I will own yesterday, tomorrow and tonight. What am I?
I am a ship that can be made to ride the greatest waves. I am not built by objects, but built by minds. What am I?
No matter how little or how much you use me, you change me every month.