There is no definitive answer on this.

Remember the reason you want to enter ratio put is

1: You expect stock to have weakness initially but followed by a bounce later

2: Even if stock does not move as you expected and continue to drop without bounce, you are ok to have the stock to be assigned to you at the lower price

If neither of this condition is true, you should NOT use ratio put

Within this strategy, you need to have some expectation on how long #1 will last and set your strike expiration timing accordingly.