Personally, I think 2-3 hours continous watching and total 6-7 hours watching per day (provided there is sufficient time gap between both session) shouldn't cause any burn in even after 2-3 years. All latest oleds have panel maintenance options, which can be run, say every 15 days to take care.
As per my experience, for OLED, only thing to note is day time viewing. If room is bright with open windows, no matter, how much brightness is cranked up, there is always some reflection seen on TV screen. But no LED/LCD can come close to an OLED TV watching experience during night time even with lights on. It's a complete different experience. Do ensure that you can sufficiently darken your room (using dark curtains) during day time viewing for optimum experience.
However, you made a good choice of going towards 65". For true cinematic experience, 65" is a must, even for a viewing distance of 10ft. When watching movies with black bars (which is typical for most movies), with 55inch the screen feels smaller very soon. With 65" even with black bars, the screen real estate is still immersive.
Do wait for Diwali discounts. You should get good deal. If you don't require attached sound bar, you can consider Panasonic fz950 too.