What does slow as the dickens mean?

Answer 1

The term "the dickens" means "to the point of ridiculousness"

Therefore saying "slow as the dickens" means you are being ridiculously slow

(Writer Charles Dickens was known for the fact that is his books he would often take a minor detail and exaggerate it for sake of comedy)

Answer 2

The phrase "slow as the dickens" is a colloquial expression used to emphasize that something is moving very slowly or taking a long time to complete. It is often used to describe a situation where progress or action is noticeably sluggish.