This should be the process:

1. Member Registers
2. Time Set To 24 hours past current time
3. Saved in Database
4. Email sent with a link that has a special confirmation number/hash
5. When they load the page to confirm, it check the database if 24 hours has past
6. If it is 24+, you can delete the account and tell them their time is past; or if it is 24- confirm account.