If March equinox is on 20th March (see the table in the link), according to it, when is the time that the sun enters Taurus? Is it on April 19 or April 20?
Guy Ottewell makes a comprehensive Astronomical Calendar each year. From the 2020 edition:
8959.117 Apr 19 SUN 15 Sun enters the astrological sign Taurus, i.e. its longitude is 30°
That's 2020-04-19 ~15h UT, which falls on April 20 in far eastern terrestrial longitudes and April 19 everywhere else. The next such event is 1 tropical year (365d 5h 49m) later.
8983.315 May 13 Wed 20 Sun enters Taurus, at longitude 53.48° on the eclip- tic
The Sun enters the constellation at 2020-05-13 ~20h UT, which falls on May 14 in Asia, Australia, etc., and May 13 everywhere else. This event recurs 1 sidereal year (365d 6h 9m) later. In that time, the ecliptic longitude of the constellation boundary increases by 0.014°.