Hi,

SQL Server by default will not store the Last login time in any system
tables.

But you could go for any of the below 2 approaches to attain this:-

1. Enable the audit level for successful login and Faile Logins using
Enterprise manager ... SECURITY tab. This will put all the
  successful and failed logins to sql server in sql server error log. You
could open the log and identify the last login time.

2. Write a stored procedure and read the Master..sysprocesses table every 1
minute (use SQL Agent jobs)  and put it into a user defined table.
    Later you could read this table to identify the last login time..

Thanks
HARI
SQL Server MVP