One!
243 days
One lunar day equals 28 earth days
There is one day in a leap day. It adds an extra day to February so that it has 29 days and the year has 366 days.
Just the one day.
one day
one day on venus is 59 earth-days long
one day!
This is planet Earth, so one Earth day is one day on this planet.
243 days
17 weeks and one day.
6 days
One seventh. There are seven days in a week.