【Data charge】Does the data I purchased have an expiration date?
Yes. The top up data is valid for 62 days from the charge date.
Validity Period Information
The data purchased through Data Charge, if it is within its validity period, can also be used in the next month and beyond, after all monthly data of your plan is used up.
If you charge a data within 24 hours after the expiration, you can carry over the data amount that has expired.
For your reference: Data expiration date, excepting monthly plan data.