KF does not have any black-out dates, and your friend can use his KF miles for upgrade so long as his paid economy class ticket is eligible for mileage accrual (that is, it should not be booked on Classes - V, Q, G, N or T).
However, SIA has restricted the number of seats that are available for upgrading or award. So it is best that your friend call them immediately to make a reservation. He can waitlist if there is no seats available for upgrade.