This is done in server console, configure this server, log on as admin, step thru & select always connected. Note that your modem will redial many times if the phone line or ISP connection develops a fault, and you will incurr all the call connection costs.
Alternatively to be able to alter the actual time connected when using the long, medium short settings, you can create custom templates. Search on "diald.filter", all dates and you will find what you need.
Regards
Ray