Under promise and over deliver.
Is it lying or a great business tactic?
I'm going with the latter for these reasons:
✔ You always get a built in buffer in case you need more time.
✔Surprise and delight. Your customer feels great getting something earlier than expected. Just think how you feel when an Amazon package arrives a day early.
✔ You are always early in the customer's eyes.
Now, sometimes over delivering can be more than you bargained for.