How many of the whole zodiac constellations can be seen in one single night? As far as I understand, since the the 12 zodiac constellations (astrological signs) 'surround' the earth, hence it's possible to see by naked eyes a group of 6 astrological signs (only) simultaneously - from one hemisphere. 

Assuming it's correct, my question is how many of the 12  zodiac constellations are possible to see in one single night? 

Since the earth moving constantly, it seems that the answer depends on the time and season, but assuming that the day and the night are equal in time (March 21th), what will be the answer? To my logic it should be 12 but I am not sure about it.
Running a simulation in Stellarium, on March 21st, you can just about see Pisces at about 7pm, but it is setting, and at 5am Aquarius is just rising, before being hidden by the sun. The sun is "in Pisces" on the 21st (the astrological houses have not been updated) but it is a pretty big constellation!

This means that you can see, or partly see all the zodiac constellations.  Although Pisces and Aquarius are not fully visible, but you can see the other 10 at some point during the night.