He did have much time to reflect since he died in November 1940, after having seen France and most of Western Europe fall and Britain under the blitz as a result of his appeasement policy.
When Chamberlain was meeting with Hitler he was already quite ill...perhaps that colored his judgement?
I think people are too harsh on Chamberlain. If you ever get to watch the famous moment where he waved that useless note from the german government and famously declared “peace in our time”, he sounds like a complete idiot - with the benefit of hindsight. BUT, just listen to everyone cheer when he did that. He wasnt the only one who was an appeaser. He just got to carry the can for everyone else who put peace in front of honor