Tickets to the Shanghai Oriental Pearl Tower and Huangpu River Cruise

I just want to visit the Tower at night on Friday 20th of April and go up as high as possible. Which Kind of ticket should I buy? When I have bought the ticket can I visit the Tower at any time, or just at a time mentioned on the ticket?
Can I buy separately 2 tickets for Satureday 21th of April for the H-river-cruise at night without the Tower?