If your date field are formatted as datetime field types, then converting them to string fields will allow them to be used as graph labels. You can convert to/from a datetime field using the datetime tool (in the Parse tool category). If you use a different date format and are worried about keeping your records in order: use a RecordID tool and a sort tool to retain the original order.
In the attached example, I entered a string field, converted to a datetime type and back to string before using them for graph labels. I also recommend using the Charting tool and not the deprecated Chart tool.
