The data is the output of TimeGapSplit.summary(df)

From here
https://github.com/koaning/scikit-lego/blob/main/sklego/model_selection.py

The dataframe supplied to summary is quite trivial. Think your example + some datetime column

Hey 🙂
What data do you have for the dataframe? Couldn't reproduce it with:
df = pd.DataFrame( { "num_legs": [2, 4, 8, 0], "num_wings": [2, 0, 0, 0], "num_specimen_seen": [10, 2, 1, 8], }, index=["falcon", "dog", "spider", "fish"], )