Lets say I have a file called functions.php, and it has two separate functions inside:
One would get the time
And the other would get the date
How will I
You don't specify in jQuery what function to execute in PHP. What you do is request a document, possibly with a query string, and read the results. Your functions.php script is responsible for executing whatever is requested.
So, you might from jQuery request functions.php?fn=time
in one place and functions.php?fn=date
in another. Then, in functions.php, you would examine the query string and execute the appropriate function for what was requested, returning the results to jQuery.