I was injured six weeks ago. Last week the P.L insurer accepted liability. So my wages and bills are being paid.
How long does my employer have to keep my job open, or do they have to take me back on light duties.

What country or state are you in? Were you injured at work or while working? You said it was a PL claim so more than likely if you werent injured at work then they dont have to keep your job open or provide suitable duties unless they want to out of the goodness of their heart!