The other gospels provide more and less detail, similar to testamony given by different witnesses at a trial. Matthew provides a little more detail in the timing. For instance, the others do not mention the angel rolling back the stone, but in the other narratives the stone is rolled back without explaining the how. Different witness, different details, none contradicting the other.
Again, the Scriptures plainly state that the tomb was already empty. Does this somehow shake your faith, whether it was Friday, Saturday, Sunday or Monday? I doubt that the day matters at all, it is the event that is celebrated.
It matters in that Jesus had stated that he would be raised on the third day:
Mt 16:21, 17:23, 20:19, 27:64 (understood by the Jewish leadership); Lk 9:22, 13:32, 18:33 (again, understood by the Jewish leadership), 24:7, 24:46
The when is important as it seals His claim to be Messiah and God.
Third day from when? If it is in the usage of today, that would put it on Monday. If your mailman tells you on Friday that he will return with a package in three days, when will you expect to see him?