diff --git a/src/entities/entities.ts b/src/entities/entities.ts
index ad53891..79acaae 100644
--- a/src/entities/entities.ts
+++ b/src/entities/entities.ts
@@ -1,8 +1,9 @@
-export interface IEntityWithId {
+export interface IEntityWithIdAndOptionalTimestamp {
   id: string;
+  millisecondsSinceEpoch: number;
 }
 
-export interface ISystem extends IEntityWithId {
+export interface ISystem extends IEntityWithIdAndOptionalTimestamp {
   name: string;
 }
 
@@ -11,20 +12,20 @@ export interface ICoordinates {
   longitude: number;
 }
 
-export interface IRoute extends IEntityWithId {
+export interface IRoute extends IEntityWithIdAndOptionalTimestamp {
   name: string;
   color: string;
   polylineCoordinates: ICoordinates[];
   systemId: string;
 }
 
-export interface IStop extends IEntityWithId {
+export interface IStop extends IEntityWithIdAndOptionalTimestamp {
   name: string;
   systemId: string;
   coordinates: ICoordinates;
 }
 
-export interface IShuttle extends IEntityWithId {
+export interface IShuttle extends IEntityWithIdAndOptionalTimestamp {
   coordinates: ICoordinates;
   name: string;
   routeId: string;