diff --git a/apps/workflow/api/src/main/java/org/onosproject/workflow/api/TimerChain.java b/apps/workflow/api/src/main/java/org/onosproject/workflow/api/TimerChain.java
new file mode 100644
index 0000000..33c6aa3
--- /dev/null
+++ b/apps/workflow/api/src/main/java/org/onosproject/workflow/api/TimerChain.java
@@ -0,0 +1,223 @@
+/*
+ * Copyright 2018-present Open Networking Foundation
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.onosproject.workflow.api;
+
+import java.util.Date;
+import java.util.PriorityQueue;
+import java.util.Timer;
+import java.util.TimerTask;
+
+/**
+ * Class for time chain timer.
+ */
+public class TimerChain {
+
+    private PriorityQueue<TimerChainTask> taskQueue = new PriorityQueue<>();
+
+    private Timer impendingTimer;
+    private TimerChainTask impendingTask;
+
+    /**
+     * Schedules timer event.
+     * @param afterMs millisecond which time event happens.
+     * @param runnable runnable to be executed after 'afterMs'
+     */
+    public void schedule(long afterMs, Runnable runnable) {
+        schedule(new Date((new Date()).getTime() + afterMs), runnable);
+    }
+
+    /**
+     * Schedules timer event.
+     * @param date date which timer event happens.
+     * @param runnable runnable to be executed on 'date'
+     */
+    public void schedule(Date date, Runnable runnable) {
+        schedule(new TimerChainTask(this, date, runnable));
+    }
+
+    /**
+     * Schedule timer chain task.
+     * @param task task to be scheduled.
+     */
+    private void schedule(TimerChainTask task) {
+        synchronized (this) {
+            if (taskQueue.size() == 0) {
+                scheduleImpending(task);
+                return;
+            }
+
+            if (task.date().getTime() < head().date().getTime()) {
+                impendingTimer.cancel();
+                impendingTask.cancel();
+                TimerChainTask prevImpendingTask = pop().copy();
+                taskQueue.offer(prevImpendingTask);
+
+                scheduleImpending(task);
+            } else {
+                taskQueue.offer(task);
+            }
+        }
+    }
+
+    /**
+     * Schedule impending timer task.
+     * @param task impending timer chain task
+     * @return timer chain task
+     */
+    private TimerChainTask scheduleImpending(TimerChainTask task) {
+        taskQueue.offer(task);
+        Timer timer = new Timer();
+        this.setImpendingTask(task);
+        this.setImpendingTimer(timer);
+        timer.schedule(task, task.date());
+        return task;
+    }
+
+    /**
+     * Gets impending timer.
+     * @return impending timer
+     */
+    public Timer implendingTimer() {
+        return impendingTimer;
+    }
+
+    /**
+     * Sets impending timer.
+     * @param impendingTimer impending timer
+     */
+    public void setImpendingTimer(Timer impendingTimer) {
+        this.impendingTimer = impendingTimer;
+    }
+
+    /**
+     * Gets impending timer task.
+     * @return impending timer task
+     */
+    public TimerTask impendingTask() {
+        return impendingTask;
+    }
+
+    /**
+     * Sets impending timer task.
+     * @param impendingTask impending timer task
+     */
+    public void setImpendingTask(TimerChainTask impendingTask) {
+        this.impendingTask = impendingTask;
+    }
+
+    /**
+     * Gets head of timer chain task queue.
+     * @return timer chain task
+     */
+    public TimerChainTask head() {
+        if (taskQueue.size() > 0) {
+            return taskQueue.peek();
+        } else {
+            return null;
+        }
+    }
+
+    /**
+     * Pops head of timer chain task queue.
+     * @return timer chain task
+     */
+    public TimerChainTask pop() {
+        if (taskQueue.size() > 0) {
+            return taskQueue.poll();
+        } else {
+            return null;
+        }
+    }
+
+    /**
+     * Class for timer chain task.
+     */
+    public static class TimerChainTask extends TimerTask implements Comparable<TimerChainTask> {
+
+        private final TimerChain timerchain;
+        private final Date date;
+        private final Runnable runnable;
+
+        /**
+         * Constructor of timer chain task.
+         * @param timerchain timer chain
+         * @param date date to be scheduled
+         * @param runnable runnable to be executed by timer
+         */
+        public TimerChainTask(TimerChain timerchain, Date date, Runnable runnable) {
+            this.timerchain = timerchain;
+            this.date = date;
+            this.runnable = runnable;
+        }
+
+        /**
+         * Gets date.
+         * @return date of timer chain task
+         */
+        public Date date() {
+            return this.date;
+        }
+
+        /**
+         * Gets runnable.
+         * @return runnable of timer chain task
+         */
+        public Runnable runnable() {
+            return this.runnable;
+        }
+
+        @Override
+        public void run() {
+
+            TimerChainTask nextTask;
+            synchronized (timerchain) {
+                if (timerchain.impendingTask() != this) {
+                    System.out.println("Invalid impendingTask");
+                    runnable().run();
+                    return;
+                }
+
+                timerchain.implendingTimer().cancel();
+                timerchain.pop();
+
+                nextTask = timerchain.head();
+
+                if (nextTask != null) {
+                    Timer nextTimer = new Timer();
+                    this.timerchain.setImpendingTask(nextTask);
+                    this.timerchain.setImpendingTimer(nextTimer);
+                    nextTimer.schedule(nextTask, nextTask.date());
+                }
+            }
+
+            runnable().run();
+
+        }
+
+        @Override
+        public int compareTo(TimerChainTask target) {
+            return date().compareTo(target.date());
+        }
+
+        /**
+         * Copies timer chain task.
+         * @return timer chain task
+         */
+        public TimerChainTask copy() {
+            return new TimerChainTask(timerchain, date, runnable);
+        }
+    }
+}