How long should it take to solve a hard Sudoku?

Related questions

1. Is there a mathematical way to solve Sudoku?
2. Are some Sudoku puzzles unsolvable?
3. What is the cell rule in Sudoku?
4. Can Sudoku increase IQ?
5. What are good sudoku times?
6. Are there patterns in Sudoku?
7. What is the hardest sudoku puzzle ever?
8. Is there a formula to solve Sudoku?
9. Is sudoku good for brain?
10. How can I play Sudoku for free?

Tags

1. #expertise
2. #skill
3. #longer
4. #larger
5. #between
6. #minutes
7. #hours
8. #puzzles
9. #depending
10. #usually
11. #sudoku
12. #three
13. #complete
14. #puzzle
15. #difficulty
16. #upwards
17. #these