I have no idea on the time, but I had most of what I wanted by the time I got to Raithwall's Tomb and I didn't level all that much. As for making characters clones, for each character I picked what I felt would benefit them the most. The reason they became clones is because the game does not reward diversity in character setup.

If the game had encouraged having a varied party but still had the option of making clones it would be a little different.

I am really pointing out two flaws in the game, one that there is no reason not to make people clones, (in my opinion clones are the best way to go) and the fact that at the end of the game all the characters must become clones.