Timer class in PHP OOP
Never ever use var. That's a deprecated form of public;
Avoid using public on your properties, you want to have controll about the value of every property in your class;
If you use protected or private doesn't make much sense. Protected means it can't be accessed from the outer scope, but it can be accessed from another class which extends this class. Private means it can only be accessed from the class where it is defined.

I like to have getters/setters for every property and never use $this-&gt;property directly inside my class, some other don't like that. See also this article by Fabien Potencier: "Pragmatism over Theory: Protected vs Private";
The :: operator, or T_PAAMAYIM_NEKUDOTAYIM, should only be used by accessing class constants and static vars/methods;
Avoid using static vars/methods;
Use $this-&gt;method() or $this-&gt;property to access properties from the inside of a class. It works just like you use it outside the class, except that you use the $this variable (which contains a reference to the current instance of the class).