Quick response.........Not sure about the time of year, Ive only kited in Fiji once and that was in Sept / Oct.
I spent a few days in Denarau at the Sofitel Resort just up the road from the Raddisson, this was just a stop over before heading to Malolo Island. However I did get a few sessions directly out the front of the resort on Denarau. Its not the best, choppy slop, water isnt very clear etc, but id rather be out kiting in those conditions than laying around a pool.
Do a search, more than enough info here on Seabreeze regarding Fiji, all your questions should be answered with a little research

This pic is out the front of the Sofitel in Denarau (Denarau Island in the background). If there is wind, and depending on direction, pretty sure you could kite from any of the beaches in front of the Denarau resorts.