The date and time at which Activity started.
restriction of DateTimeForm
| minLength | 0 |
| pattern | \d{2}/\d{2}/\d{4} (20|21|22|23|[0-1]?\d):[0-5]?\d |


| minLength | 0 |
| pattern | \d{2}/\d{2}/\d{4} (20|21|22|23|[0-1]?\d):[0-5]?\d |