Specifically for weddings and other events that have a time schedule, it makes sense to sort the sub-galleries in a specific order. To set this order, open the parent gallery in which the sub-galleries are located and click on the three items next to the gallery name in the side menu on the left. Select "Sort Sub-Galleries" and change the mode from "Sort Alphabetically" to "Sort Manually". Now you can set the order freely by drag & drop.