Code B is better, for all the reasons posted above. It also shows better logic, through your use of 1 return of s.
But, the code does slightly different things. Code A won't append anything to s if s is = to 3, whereas Code B will. Is this a mistake?
Useful function to retrieve difference in times
The best PHP resource
A good PHP FAQ
PLEASE remember to wrap your code in [PHP] tags.
// Replace this
// With this
// Then check for values/forms. Some IE versions don't send the submit button
Always code as if the guy who ends up maintaining your code will be a violent psychopath who knows where you live.