30 minutes? Man, you have a strong back. Or maybe just a different back problem than I have.

With some hyperbole I'd say "immediately", but to factual I can report that in my case back pain sets in between 2 and 4 minutes if I don't use a pillow, and a second one for the neck (because no headrest). Fortunately they have pillows already on the seats in J (and it's easy to ask for a second one for the neck), and in Y/on domestic flights where they don't have any on the seats one can always ask for two of them when they pass through the cabin before taxiing. My 2-4 minute benchmark comes from the times when I board early and don't have a chance yet to ask for a pillow, so it may take 15-20 minutes to have pain relief...

Back to the planes: having flown on the A220 many many times now - it has become LX' work horse on the ZRH-CDG and ZRH-LCY runs - I must say that I like that plane a lot, at least in the way they have done it. VERY VERY large overhead bins, whose full potential is wasted because of people who don't get how to place their luggage (vertical), they have extended and very comfortable legroom for the first 8 or 10 rows, and in J class they always keep one neighbouring seat free. The LX seat is miles better than the NEO seat, but not as comfortable as the most recent AF Euro seats. The combination of the latest AF seat with the LX legroom and 1-2 config in J, I think I'll like that plane, at least not less than the current A319-A321 fleet.