You wont notice any difference in performance changing your oil at those intervals. BMW's and others take their cars past that for changes. Some people with synthetic go even longer. Unless your oil has turned to glue, you wont notice any differences, and unless your timing belt is slipping, you wont notice any differences there either.

Using Visual inspection for your timing belt is like using it to check your tire pressures. Unless its really falling apart, you wont be able to tell when its time to be changed.