How is the validity period of a phone notification service package calculated?

The phone notification service takes effect immediately after you pay for it and will be valid for 29 days plus 23 hours 59 minutes and 59 seconds thereafter. For example, a user paid for a 30-day phone notification service package at 12:30 on October 1, 2018. The user's service would be valid until 12:30:59 on October 31, 2018.