Regarding בענין קריאת ההגדה בשבת הגדול Rabbi Grossman writes:
I believe the simple understanding of the Gra is like this: You can prepare your matza and remove your Haggada whenever before Passover, there just is no accomplishment if you do either specifically the afternoon before Passover.He only believes in a positive performance if it achieves some sort of zecher (zeicher?) lamikdash. Some believe it is best to bake matza then. some believe it is best to review maggid then. Ka mashmalan, there is no such issue. but if that is the only time you have to make matza or review, then mah tovumahnai’m.