Defining Time Constraints of a Task 
Time constraints refer to the activation, start, completion and expiration time of the task. You can define these times and deadlines by one of the following options:
Use a fixed reference time and an offset.
Use an expression to evaluate absolute time of type xsd:dateTime.
Caution
If you use context nodes in your expression from different namespaces with equal names, you have to declare the namespaces of these nodes. To solve the name conflict you can define a name prefix for the namespace. This declaration has the following syntax: xmlns:<prefix_name>="namespace_name".
You can make the task raise critical exception when a start or completion deadline is reached.
Define an Activation Time of a Task
For more information, see Defining an Activation Time of a Task.
Define a Default Start Deadline of a Task
For more information, see Defining a Default Start Deadline of a Task.
Define a Default Completion Deadline of a Task
For more information, see Defining a Default Completion Deadline of a Task.
Define a Default Expiration Time of a Task
For more information, see Defining a Default Expiration Time of a Task.