The tube from Edgware Road to Waterloo last night was a minute late. Didn't cause me to miss the connecting train to Hersham, though, so I won't charge for it. I will charge for that train being a minute late, however. £2.50.
This morning, the train from Hersham actually arrived in Waterloo four minutes early. This allowed me to get an earlier connecting tube to Edgware Road, which ran on time, so I arrived three minutes early at my final destination (work).
Taken together, that means I have to refund TfL £5. Well played, TfL.