Join Date: May 2012
Location: Munich, Algarve, Sussex or S.F Bay Area
Programs: Mucci, BA Gold, A3*Gold, AA Plat, HH Gold, IHG Plat Amb, Marriott Plat
Posts: 4,163
I think how significant 2 or 4 hours is depends on the traveller and is not really specifically for BA to set. If a 2 hour change means you cannot make a meeting then even that is significant.
In the past, I have shifted flights to months later due to a 1:30 change that clearly no longer served my purpose. That is almost certainly even easier to justify with 4 hours. I would stick to your guns and insist on a free change or cancellation.
In case BA doesn't play ball, couldn't you request an FTV (Future Travel Voucher) under the COVID book with confidence scheme and redeem that for another ticket at a later date?