Well, if you are looking for a quick fix you can throw this in a .js file and add it to your plugins list. Just change the default value 16 to something higher to make the window wait longer before changing.
JavaScript:
Window_BattleLog.prototype.messageSpeed = function() {
// Change 16 to something higher to increase the wait time between logs.
return 16;
};
If your looking for something a little more dynamic, like plugin commands or even notetags, I'd say check out Yanflys Action Sequence Packs, they have some awesome features packed in there.