diff --git a/src/notifications/schedulers/ETANotificationScheduler.ts b/src/notifications/schedulers/ETANotificationScheduler.ts
index 480fc2b..76c6027 100644
--- a/src/notifications/schedulers/ETANotificationScheduler.ts
+++ b/src/notifications/schedulers/ETANotificationScheduler.ts
@@ -20,8 +20,10 @@ export interface ScheduledNotificationData {
   secondsThreshold?: number;
 }
 
+type DeviceIdSecondsThresholdAssociation = { [key: string]: number };
+
 export class ETANotificationScheduler {
-  public readonly secondsThresholdForNotificationToFire = 180;
+  public readonly defaultSecondsThresholdForNotificationToFire = 180;
 
   constructor(private repository: GetterRepository,
               private appleNotificationSender = new AppleNotificationSender()
@@ -37,9 +39,10 @@ export class ETANotificationScheduler {
    * An object of device ID arrays to deliver notifications to.
    * The key should be a combination of the shuttle ID and
    * stop ID, which can be generated using `TupleKey`.
+   * The value is a dictionary of the device ID to the stored seconds threshold.
    * @private
    */
-  private deviceIdsToDeliverTo: { [key: string]: Set<string> } = {}
+  private deviceIdsToDeliverTo: { [key: string]: DeviceIdSecondsThresholdAssociation } = {}
 
   private async sendEtaNotificationImmediately(notificationData: ScheduledNotificationData): Promise<boolean> {
     const { deviceId, shuttleId, stopId } = notificationData;
@@ -77,7 +80,7 @@ export class ETANotificationScheduler {
     }
 
     const deviceIdsToRemove = new Set<string>();
-    for (let deviceId of this.deviceIdsToDeliverTo[tuple.toString()].values()) {
+    for (let deviceId of Object.keys(this.deviceIdsToDeliverTo[tuple.toString()])) {
       const deliveredSuccessfully = await this.sendEtaNotificationImmediatelyIfSecondsRemainingBelowThreshold(deviceId, eta);
       if (deliveredSuccessfully) {
         deviceIdsToRemove.add(deviceId);
@@ -85,12 +88,12 @@ export class ETANotificationScheduler {
     }
 
     deviceIdsToRemove.forEach((deviceId) => {
-      this.deviceIdsToDeliverTo[tuple.toString()].delete(deviceId);
+      delete this.deviceIdsToDeliverTo[tuple.toString()][deviceId]
     });
   }
 
   private async sendEtaNotificationImmediatelyIfSecondsRemainingBelowThreshold(deviceId: string, eta: IEta) {
-    if (eta.secondsRemaining > this.secondsThresholdForNotificationToFire) {
+    if (eta.secondsRemaining > this.defaultSecondsThresholdForNotificationToFire) {
       return false;
     }
 
@@ -106,13 +109,20 @@ export class ETANotificationScheduler {
    * @param deviceId The device ID to send the notification to.
    * @param shuttleId Shuttle ID of ETA object to check.
    * @param stopId Stop ID of ETA object to check.
+   * @param secondsThreshold Value which specifies the ETA of the shuttle for when
+   * the notification should fire.
    */
-  public async scheduleNotification({ deviceId, shuttleId, stopId }: ScheduledNotificationData) {
+  public async scheduleNotification({ deviceId, shuttleId, stopId, secondsThreshold }: ScheduledNotificationData) {
     const tuple = new TupleKey(shuttleId, stopId);
     if (this.deviceIdsToDeliverTo[tuple.toString()] === undefined) {
-      this.deviceIdsToDeliverTo[tuple.toString()] = new Set();
+      this.deviceIdsToDeliverTo[tuple.toString()] = {};
+    }
+
+    if (secondsThreshold !== undefined) {
+      this.deviceIdsToDeliverTo[tuple.toString()][deviceId] = secondsThreshold;
+    } else {
+      this.deviceIdsToDeliverTo[tuple.toString()][deviceId] = this.defaultSecondsThresholdForNotificationToFire;
     }
-    this.deviceIdsToDeliverTo[tuple.toString()].add(deviceId);
 
     this.repository.unsubscribeFromEtaUpdates(this.etaSubscriberCallback);
     this.repository.subscribeToEtaUpdates(this.etaSubscriberCallback);
@@ -128,12 +138,12 @@ export class ETANotificationScheduler {
     const tupleKey = new TupleKey(shuttleId, stopId);
     if (
       this.deviceIdsToDeliverTo[tupleKey.toString()] === undefined
-      || !this.deviceIdsToDeliverTo[tupleKey.toString()].has(deviceId)
+      || !(deviceId in this.deviceIdsToDeliverTo[tupleKey.toString()])
     ) {
       return;
     }
 
-    this.deviceIdsToDeliverTo[tupleKey.toString()].delete(deviceId);
+    delete this.deviceIdsToDeliverTo[tupleKey.toString()][deviceId];
   }
 
   /**
@@ -147,7 +157,7 @@ export class ETANotificationScheduler {
     if (this.deviceIdsToDeliverTo[tuple.toString()] === undefined) {
       return false;
     }
-    return this.deviceIdsToDeliverTo[tuple.toString()].has(deviceId);
+    return deviceId in this.deviceIdsToDeliverTo[tuple.toString()];
   }
 
   /**
@@ -158,7 +168,7 @@ export class ETANotificationScheduler {
     const scheduledNotifications: ScheduledNotificationData[] = [];
 
     for (const key of Object.keys(this.deviceIdsToDeliverTo)) {
-      if (this.deviceIdsToDeliverTo[key].has(deviceId)) {
+      if (deviceId in this.deviceIdsToDeliverTo[key]) {
         const tupleKey = TupleKey.fromExistingStringKey(key);
         const shuttleId = tupleKey.tuple[0]
         const stopId = tupleKey.tuple[1];