my ford f150 hs an oil change due in another 2 weeks but since i have been driving my GC lately it only has like 200 miles on it! I dontknow if it matters but its val durablend 5w20 oil thats in the truck.
If the truck is in storage do an OC with 10w-40 or 15w40. Drive it for 30 minutes before you park it. When you start using the truck again change back to 5w-20.
I would think you are good for 6 months, unless it has been abused with very short trips only. But if warranty requires 3 months, then you better do it. I always ran the Aerostar 6 months to get 3000 miles and it does not seem to have hurt.