Discrete avalanching is the dominant motion of granular beds in industrial rotary kilns. The avalanche time is an important parameter influencing the heat- and material transfer inside the kiln. Experiments are conducted on a rotating cylinder to measure the time evolution of avalanches. Nonspherical particles (rice) and low filling degrees are used in order to simulate the operating conditions in industrial kilns. The difference between the average critical angle and stop angle of the avalanche is found to be in the range of 7 degrees-9 degrees, i.e., much higher values than ever reported in literature. As the filling degree is three times increased, the average critical angle is found to be approximately constant, whereas the average stop angle is slightly increased and the avalanche time is increased by 20%. For all experimental configurations, the average avalanche time occupies about 35 %- 38 % of the total circle time (elevation time plus avalanche time). Experimental data are used to test theoretical models from different authors. Comparison demonstrates that the models proposed by Mellmann and Davidson et al. can predict well the increasing tendency of average avalanche time with filling degrees. The former has higher accuracy with errors less than 5 % for all experiments. Results of this work are useful for kiln design and further theoretical studies on dynamics of granular avalanches.