Time-resolved phosphorescence quenching measurements with a terbium complex-as lumophore and methyl viologen and bromphenol blue quenchers allow one to monitor processes in ionic and nonionic water in oil microemulsions in the long (millisecond) time range. We interpret the decay in this time range as exchange of quencher between clusters of microemulsion droplets. We show that material exchange due to this clustering starts below the percolation threshold, the rate increasing along the percolation transition. The activation energies, which are formally negative in the nonionic system, are discussed with respect to the processes involved in the fusion of droplets and clusters. Comparison of ionic AOT- and nonionic Igepal-stabilized microemulsions gives evidence that the droplets in the ionic system maintain their compartmental structure even at temperatures above the percolation threshold.