I often say "What?" even though I heard what the person said only to have more time to think about what my real answer will be.
What's the point in lying about not hearing someone?
I don't want to be held accountable for my actions right away, I need to think it through.
I'm sure people will be understanding if you want to take time to think of an answer. Just be honest and tell them you need a moment to think and they will be patient and wait. That way there's no need to lie.
It's fine as long as I wait 3 seconds before talking.
Taking a couple seconds to formulate a response is definitely a better alternative to lying to someone. People are understanding and won't be upset if you need a couple seconds to think before responding to their statement.