The min. Loan tenor is 5yrs. However, this depends on the loan amount, age of property, age of applicaant & the repayment ability.
70% is just a maximum Bank offer. You may borrow lower than 70%.
If you borrow HK1,000,000. Every month pay HKD10K. According to the interest offer by the Bank, 2.75%p.a, you have to repay for 10yrs. (every month pay HKD9,518)