Full Moon, doesn't matter what sign. Capricorn would be great but it can be any sign, as long as it's the day before or the day of a Full Moon.
If in an emergency do it at any time as long as the moon is not void, and then re-do it at the full moon.
No, you do not have to do it for 40 days, unless you have very weak power. One time should suffice, or 3 days, or 9 at most.