They claim, that Christ died on Wednesday, and therefore, John 19:31 would mean the following "Thursday" was this high Sabbath day. Problem is, that is NOT the Biblical definition of a high Sabbath day. A high Sabbath occurred when a feast day (In this case it was the Feast of Unleavened Bread) fell on the 7th day weekly Sabbath. Since the Seventh Day is already considered a Sabbath, and the feast days are considered "annual" Sabbaths, (See Lev. 23:23-38) when they fell on the same day, that day would then be considered a HIGH Sabbath day. A "Thursday" or "5th day" of the week would NEVER be considerd a High Sabbath. That is an absolute impossiblity.
PLUS.. notice this, in Luke 23:56 it states the woman did not prepare the body of Jesus on Friday because they, "...rested the sabbath day according to the commandment." Biblical FACT is, the Commandments speak of the Seventh Day Sabbath, not the annual feast day sabbaths.
PLUS, Christ was put to death on the "preparation day," of the week and the preparation day was never on a Wednesday. In all the pages of biblical history, as well as biblical jurisprudence, the preparation day has always been and will always continue to be Friday. This is graphically confirmed in Mark 15:42-43 where is states, "And now when the even was come, because it was the preparation, that is, the day before the sabbath, Joseph of Arimathaea, an honourable counsellor, which also waited for the kingdom of God, came, and went in boldly unto Pilate, and craved the body of Jesus."