Need help with db script, and daily routines

Hello,

I have 2 tables:

In one I log the user name of a web site user like this:

Name Access time
"makost0001" " 2007-04-19 15:09:19"
"makost0001" " 2007-04-19 15:09:19"

In the other I have the user name his group and the expiry date of his
account.

Name Group Expiry date
"makost0001" "book" "2013-04-05 09:41:25.357677"

When the user accesses the web site for the first time I need to change the
expiry date
to < today > + 3 years.

Problem is I need to do this on a regular basis once a day to avoid table
locks. And also how do I tell the program to find the earliest access time
of a user? Like shown above there a multiple
entries for the same time & user because of the multiple requests. :o(

Should I have a field in the first table like <ignore this entry forever>
when an expiry date is already set?

I'm pretty new to db programming and especially to PostgreSQL. Can somebody
please help?

Cheers,
Pete