We bought a brand new Ford Escape 3 years ago. The warranty booklet states that the car has to undergo maintenance every 3 months of 5,000 kilometers whichever comes first. Since we have 2 cars, obviously the 3 months became the rule. When we asked what would happen if we don't follow the 3 months schedule, the service advisor said it will void the warranty. What a coincidence, when the 3-year warranty expired this year, there was something wrong with the car's air conditioning system. I was dejected because we were spending so much for that 3-month maintenance schedule and this happens. I asked the tech secretly about the need for maintenance and the honest answer I got was 6 months - maintenance check of twice a year will suffice since the car is quite new. So there, if you want to save on maintenance and your car has no more warranty, get the twice a year maintenance checkup schedule.
I have a Toyota vios and it no longer has a warranty. The chief mechanic told me that the regular checkup for my car was 4 months or 5000 kms whichever comes first. However, I also don't follow what he says regarding the regular checkup. I use the 6- month rule like you do. It's more efficient. I do think that having a regular 3 month checkup for your car is quite expensive when all they do is change the oil and the sparkplugs. Sheesh