diff --git a/app/src/handlers/demo-plc.ts b/app/src/handlers/demo-plc.ts
index 4e7fd06..24bafff 100644
--- a/app/src/handlers/demo-plc.ts
+++ b/app/src/handlers/demo-plc.ts
@@ -13,12 +13,12 @@ type DemoPlcPayload = {
 
 type DemoPlcMetric = {
   edge: string
-  timestamp: number
+  timestamp: string
   tag: string
   value: number
 }
 
-function toMetric(payload: DemoPlcPayload, timestamp: number): DemoPlcMetric {
+function toMetric(payload: DemoPlcPayload, timestamp: string): DemoPlcMetric {
   return {
     edge: EDGE,
     timestamp,
@@ -42,6 +42,6 @@ export const handleDemoPlc: TopicHandler = async (topic, payload) => {
   console.log('demo.plc.received', { topic, bytes: payload.length })
 
   const value = parseJson<DemoPlcPayload>(payload)
-  const metric = toMetric(value, Date.now())
+  const metric = toMetric(value, new Date().toISOString())
   await postMetric(metric)
 }
diff --git a/app/src/handlers/edge5-modbus-v2.ts b/app/src/handlers/edge5-modbus-v2.ts
index 8c8335e..9c40af3 100644
--- a/app/src/handlers/edge5-modbus-v2.ts
+++ b/app/src/handlers/edge5-modbus-v2.ts
@@ -54,6 +54,6 @@ export const handleEdge5ModbusV2: TopicHandler = async (topic, payload) => {
   console.log('edge5.modbus.v2.received', { topic, bytes: payload.length })
 
   const values = parseValues(payload)
-  const metrics = mapper.mapValues(values, Date.now())
+  const metrics = mapper.mapValues(values, new Date().toISOString())
   await postMetrics(metrics)
 }
diff --git a/app/src/handlers/edge5-modbus.ts b/app/src/handlers/edge5-modbus.ts
index 94abe24..99e3d84 100644
--- a/app/src/handlers/edge5-modbus.ts
+++ b/app/src/handlers/edge5-modbus.ts
@@ -8,7 +8,7 @@ const REGISTER_COUNT = 125
 
 type Edge5ModbusMetric = {
   edge: string
-  timestamp: number
+  timestamp: string
   tag: string
   value: number
 }
@@ -25,7 +25,7 @@ function assertRegisterCount(values: number[]): void {
   }
 }
 
-function toMetrics(values: number[], timestamp: number): Edge5ModbusMetric[] {
+function toMetrics(values: number[], timestamp: string): Edge5ModbusMetric[] {
   return values.map((value, index) => ({
     edge: EDGE,
     timestamp,
@@ -51,6 +51,6 @@ export const handleEdge5Modbus: TopicHandler = async (topic, payload) => {
   console.log('edge5.modbus.received', { topic, bytes: payload.length })
 
   const values = parseValues(payload)
-  const metrics = toMetrics(values, Date.now())
+  const metrics = toMetrics(values, new Date().toISOString())
   await postMetrics(metrics)
 }
diff --git a/app/src/mapping.ts b/app/src/mapping.ts
index cbbb8ca..ad41c87 100644
--- a/app/src/mapping.ts
+++ b/app/src/mapping.ts
@@ -2,7 +2,7 @@ import { readFileSync } from 'node:fs'
 
 export type MappedMetric = {
   edge: string
-  timestamp: number
+  timestamp: string
   tag: string
   value: number
 }
@@ -14,7 +14,7 @@ type MappingConfig = {
 
 export type MetricMapper = {
   edge: string
-  mapValues: (values: number[], timestamp: number) => MappedMetric[]
+  mapValues: (values: number[], timestamp: string) => MappedMetric[]
 }
 
 type MetricMapperOptions = {