Passage of time

If you watch a lot of Star Trek, you have to wonder why they all talk English.  Or they seem to know how to relate to Earthlings in a manner that an Earthling will easily understand.  For example, with the passage of time, it is always expressed in dimensions that Earthlings understand.  Such as in years, months, or days.

What could be a way to do it so that any extra-terrestrial might understand it?

Try it in half-lives.  To say it in years, use the half life of Ruthenium-106, which is about a year.  Iodine-131 is about 8 days.  Californium-254 is about two months. 

But how do you communicate the names of these isotopes?  By the number of protons and neutrons in the nucleus.  But how do you differentiate between protons and neutrons?

Yep, talking to extra-terrestrials would be a problem.