Login Welcome Page will always be at Level 0, but it is shown to any member after logging in, which may include Level 0 ones. If you want to have separate pages for each level, you can use the redirection URL.
WP Admin -> s2Member -> General Options -> Login Welcome Page -> Special Redirection URLThere you enter something like
http://example.com/welcome-%%current_user_level%% Then you can create two pages, one for each level, e.g.
http://example.com/welcome-0 restrict it at Level 0
http://example.com/welcome-1 restrict it at Level 1
I hope that helps.