About an hour, if you want/can. If not, just go ahead and eat the brown rice. Digestion is something individual. Some people have no problem in eating fruit and starch at the same meal, whereas other people get bad bloating and gas.
If you think about it, many people eat oatmeal (starch) with fruits for a meal. No biggie.
Yeah I agree, it depends on how sensitive your digestive system is. I can easily eat cooked food 30 minutes after fruit if I'm hungry that soon after. I also sometimes (not recommended) eat fruit AFTER cooked by waiting a couple hours to make sure the fruit is nearly almost out of my system. Fruit digests super quick.
Generally I wait at least 3-4 hours and never eat fruit after cooked food until the next morning. My body is really low in digestive enzymes and digestion is very sluggish so this has helped a lot.