Change at 1000km, then again put in some lousy oil and change at 2000km. This is because you actually want to wear the new parts down to correct size.
Now put in Castrol GTX (I found this one to be the best in mineral base-stock oils) and change at 10000km.
Now put in SYNTHETIC oil such as Shell Helix Ultra (the grey bottle), Castrol Magnatec, Total Quartz 9000 or ZIC XQ and then change every 20000km or every 6 months. But use very good oil filter such as VIC. Using SGP, Guard, Qaim or Leppon filters for extended drain interval is not recommended.
Even if you use simple Castrol GTX, you can (and should) change every 10000km because the owner's manual (of all cars having Suzuki G10 engine) says so. Changing any earlier without solid reason is stupidity.