When a Human Task is pending to be submitted, you can define a "Notification" for sending a reminder to the user. The "Expires At" attribute a time definition when notification is triggered. The reminder will be sent every "Expires At" value until the Human Task is submitted.

According to the documentation of JBoss BPMS 6 [1], you could specify the value "Expires At" for firing only once at a specific time using a ISO8601 pattern:

~~~
PT2S - fires once after 2 seconds
~~~

The problem is that it can not be used because in the TimeUtils the ISO8601 pattern is commented:

~~~
// ISO 8601 compliant
// private static final Pattern ISO8601 = Pattern.compile( "(P((\\d+)[Yy])?((\\d+)[Mm])?((\\d+)[Dd])?)?(T((\\d+)[Hh])?((\\d+)[Mm])?((\\d+)[Ss])?((
d+)([Mm][Ss])?)?)?" );
~~~

[1] https://access.redhat.com/documentation/en-us/red_hat_jboss_bpm_suite/6.4/html/user_guide/appe_process_elements#timing