basically oil/air filters will need to be changed after certain number of kms you run your bike not TIME (period).
the best guide for tuning times/kms will be your owners manual. also alot will depend on your enviornment, dusty conditons need more frequent air filter changes.
having said that, oil(and petrol) loose some of thier chemical properties after some time eg. long period storage etc.
plugs are a different story. depending on the state of tune of your bike, changing plugs every 4 tune ups maybe a good idea. manufacturers suggest to change every time, i personally dont agree.
when deciding when to change plugs notice its color. a light brown to tan shade is perferable. if its colorered lighter or darker.......you need a tune up in addition to new plugs
hope this helps