As you know, it is possible to enter a validity when assigning roles and privileges through the SAP Identity Management UI based on a date. With this, e.g. the assignments will be valid at the beginning of the day.
But, it is also possible to assign roles and privileges on a more fine granular base with a timestamp. You are able to supply hour, minute, and, if you want to push it further, also seconds and millis.
In a ToIdentity Store Pass, select Entry Type MX_PERSON, and add following lines in order to assign a role on 2015/08/21 on 18:15 (6:15 pm).
You could also use following timestamp to supply millis, but I do not think you need that 😉
Same is true for the VALIDFROM link attribute.