Question: If my khums year ends on February 1st but my salary is paid on, say, 28th January, will khums to be paid on it?

Answer: If it is spent by five days after the expiration of the khums year, it is not liable to khums.
Also, saving some money for possible events is not liable to khums if after paying khums, the remaining amount is not enough and the person's anxiety is not resolved. However, it is a caution to pay khums on the unused amount after the concern is resolved (by receiving the new income).