Update README.md

README.md

@@ -6368,14 +6368,14 @@ All datasets formatting follows a similar structure.
 ### Data Fields
 
 The data fields are the same among all datasets and splits.
-The datetime column is left out when no data is available.
-- `datetime`: a `timestamp[ns]` sequence, containing event datetime if available.
+The datetime column is optional and left out when no data is available.
 - `type_event`: a classification label (`int64`) sequence.
 - `time_since_last_event`: a `float64` sequence of inter-event times.
 - `time_since_start`: a `float64` sequence of event timestamps since sequence start.
 - `seq_idx`: an `int64` feature uniquely identifying sequences in the split.
 - `dim_process`: an `int64` feature representing total number of classes in the dataset.
 - `seq_len`: an `int64` feature containing sequence length.
+- `datetime`: (optional) a `timestamp[ns]` sequence, containing event datetime if available.
 
 The classification labels differ for each dataset.
 The corresponding labels for each event type can be read from metadata like this