"Few" has a specific meaning when applied to something countable. 40 is not "a few" in any common use of the word.
You don't say "It took the settlers 180 days to ride a wagon across the country, but today it only takes a few hours to drive across the country" when you meant "40 hours".
If you want to use "few", you'd use a different unit like "and now it only takes a few days". Or "And you can send a signal to that star system in a few decades".
