I'm sure you're right, but there were so many other circumstances where "är" translated as "have/has" and, viceversa, "har" turned into "am/are/is" that this becomes quite confusing.
In English, this particular sentence does sound better with "has" rather than "is". Perhaps this should qualify as "another [correct] translation".
We should probably accept both (so I'll add dygn as well), but it's a lot more idiomatic to use just dagar here.
It's a little like English can say "day" to mean either the daytime part of a day, or the day plus the night - there's just a difference in that English uses "day" for the latter meaning more frequently than Swedish does.