Found a solution, instead of boundary event, I used Timer. And before timer placed one Script Task.
Following script did the job:
org.jbpm.workflow.core.node.TimerNode timerNode =
(org.jbpm.workflow.core.node.TimerNode)
kcontext.getNodeInstance().getNode().getNodeContainer().getNode(237);
timerNode.getTimer().setPeriod(reminderInterval);
timerNode.getTimer().setDelay(reminderInterval);
reminderInterval is process variable and 237 is id of the timer node.