The 5 month Timeskip does make sense. Yoshida says a week has passed **before** Denji is knocked out again. It is never stated how long he was in prison for.

Yes the surgeons just finished chopping up Denji, but we don't know that this happened as soon as Denji went unconscious. Or maybe he regenerated so many limbs it took them 5 months. Theoretically they'd have to ensure his regeneration had completely stopped before putting him in boxes

It's stupid but it doesn't actually "break" the timeline. It doesn't contradict anything we're told

I actually do think Fujimoto's intention was for Denji to be unconscious for 5 months. He probably just forgot to state that which is why it's clarified recently