When to perform node/edge graph feature extraction?

Hi! I have a CSV file which can be converted into a DGL graph data object for an edge classification task. Before doing that, I thought of adding some features using NetworkX library. However, since after creating the graph I’m going to split it into train/val/test, then using a dataloader, I am unsure if the graph-based preprocessing should be done before the split, right after the split (before creating the dataloader), or inside/after the dataloader construction.
What’s the best way to proceed?

Thank you!