Reduce all animation timers to 200ms instead of 250ms so that they happen within the space of a leaflet zoom. Fixes #140 more details on there.

dist/MarkerCluster.css

@@ -1,6 +1,6 @@
 .leaflet-cluster-anim .leaflet-marker-icon, .leaflet-cluster-anim .leaflet-marker-shadow {
-	-webkit-transition: -webkit-transform 0.25s ease-out, opacity 0.25s ease-in;
-	-moz-transition: -moz-transform 0.25s ease-out, opacity 0.25s ease-in;
-	-o-transition: -o-transform 0.25s ease-out, opacity 0.25s ease-in;
-	transition: transform 0.25s ease-out, opacity 0.25s ease-in;
+	-webkit-transition: -webkit-transform 0.2s ease-out, opacity 0.2s ease-in;
+	-moz-transition: -moz-transform 0.2s ease-out, opacity 0.2s ease-in;
+	-o-transition: -o-transform 0.2s ease-out, opacity 0.2s ease-in;
+	transition: transform 0.2s ease-out, opacity 0.2s ease-in;
 	}

src/MarkerCluster.Spiderfier.js

@@ -231,7 +231,7 @@ L.MarkerCluster.include(!L.DomUtil.TRANSITION ? {
 		setTimeout(function () {
 			group._animationEnd();
 			group.fire('spiderfied');
-		}, 250);
+		}, 200);
 	},
 
 	_animationUnspiderfy: function (zoomDetails) {
@@ -309,7 +309,7 @@ L.MarkerCluster.include(!L.DomUtil.TRANSITION ? {
 				delete m._spiderLeg;
 			}
 			group._animationEnd();
-		}, 250);
+		}, 200);
 	}
 });
 

src/MarkerClusterGroup.js

@@ -809,7 +809,7 @@ L.MarkerClusterGroup.include(!L.DomUtil.TRANSITION ? {
 			});
 
 			me._animationEnd();
-		}, 250);
+		}, 200);
 	},
 
 	_animationZoomOut: function (previousZoomLevel, newZoomLevel) {
@@ -850,7 +850,7 @@ L.MarkerClusterGroup.include(!L.DomUtil.TRANSITION ? {
 				c._recursivelyRemoveChildrenFromMap(bounds, previousZoomLevel + 1);
 			});
 			me._animationEnd();
-		}, 250);
+		}, 200);
 	},
 	_animationAddLayer: function (layer, newCluster) {
 		var me = this;
@@ -871,7 +871,7 @@ L.MarkerClusterGroup.include(!L.DomUtil.TRANSITION ? {
 					layer.setOpacity(1);
 
 					me._animationEnd();
-				}, 250);
+				}, 200);
 
 			} else { //Just became a cluster
 				this._forceLayout();