I do a fair amount of sprouting. What you are looking for is a bud on
the tip of the grain. That tells you the grain is activated and moving
rapidly in to enzyme production mode. I haven't seen this in two hours
under any circumstances with any grain. The rate depends on
temperature, the freshness of the grain used and the hardness of the
hull. Brown rice has a hard hull. Figure 20 hours. A yogurt maker will
help speed things along.

It is possible the rice will begin to ferment. That is an additional
benefit to you.