How fast do bed sores develop?

It really depends on many things, mostly how thin his skin is. If he is in one position for a length of time he would likely develop the start of them in hours. There are various stages of the sores and the longer he's left, the further the stage would progress.

There is a lot of stuff on the internet that is basically fat-shaming diabetics for causing their own diabetes with their bad diet and lack of exercise and general lack of moral fibre. A lot of this stuff is written by non-doctors, often with a supplement or diet or training plan to sell that they claim will completely cure diabetes if only people stick to it.

I read this interesting book https://tr.im/S4PB1 that gave me a lot of useful tips about my disease and also a different perspective on the best therapeutical approach. I think you should read it too.

1

About a week plus.