I made this sudoku some month ago. My solving time now is 15 minutes, let's see if anyone can solve it under 5 minutes :)
Rules for Product Squares Sudoku:
Standard sudoku rules apply. Additionally for each gray squares the bottom cells contain a two-digit number which is the product of the numbers in the two upper cells.
For instance if the top numbers are 7-9 or 9-7 the bottom is 6-3 (stricly in this order).