diff --git a/js/src/client.ts b/js/src/client.ts
index b7ef0bee..95d0216b 100644
--- a/js/src/client.ts
+++ b/js/src/client.ts
@@ -224,8 +224,8 @@ interface CreateRunParams {
   inputs: KVMap;
   run_type: string;
   id?: string;
-  start_time?: number;
-  end_time?: number;
+  start_time?: number | string;
+  end_time?: number | string;
   extra?: KVMap;
   error?: string;
   serialized?: object;
diff --git a/js/src/langchain.ts b/js/src/langchain.ts
index ce815de9..3cf20b01 100644
--- a/js/src/langchain.ts
+++ b/js/src/langchain.ts
@@ -71,7 +71,7 @@ export async function getLangchainCallbacks(
     if (!current || visited.has(current.id)) continue;
     visited.add(current.id);
 
-    runMap.set(current.id, current);
+    runMap.set(current.id, current as Run);
     if (current.child_runs) {
       queue.push(...current.child_runs);
     }
diff --git a/js/src/run_trees.ts b/js/src/run_trees.ts
index 64cc7fb2..ba0cc866 100644
--- a/js/src/run_trees.ts
+++ b/js/src/run_trees.ts
@@ -14,7 +14,7 @@ function stripNonAlphanumeric(input: string) {
 }
 
 export function convertToDottedOrderFormat(
-  epoch: number,
+  epoch: number | string,
   runId: string,
   executionOrder = 1
 ) {
@@ -154,8 +154,8 @@ export class RunTree implements BaseRun {
   project_name: string;
   parent_run?: RunTree;
   child_runs: RunTree[];
-  start_time: number;
-  end_time?: number;
+  start_time: number | string;
+  end_time?: number | string;
   extra: KVMap;
   tags?: string[];
   error?: string;
diff --git a/js/src/schemas.ts b/js/src/schemas.ts
index 274a76bb..641f0be9 100644
--- a/js/src/schemas.ts
+++ b/js/src/schemas.ts
@@ -75,13 +75,13 @@ export interface BaseRun {
   name: string;
 
   /** The epoch time at which the run started, if available. */
-  start_time?: number;
+  start_time?: number | string;
 
   /** Specifies the type of run (tool, chain, llm, etc.). */
   run_type: string;
 
   /** The epoch time at which the run ended, if applicable. */
-  end_time?: number;
+  end_time?: number | string;
 
   /** Any additional metadata or settings for the run. */
   extra?: KVMap;
@@ -148,6 +148,10 @@ export interface Run extends BaseRun {
   /** The ID of the project that owns this run. */
   session_id?: string;
 
+  start_time: string;
+
+  end_time?: string;
+
   /** IDs of any child runs spawned by this run. */
   child_run_ids?: string[];
 
@@ -199,7 +203,7 @@ export interface RunCreate extends BaseRun {
 
 export interface RunUpdate {
   id?: string;
-  end_time?: number;
+  end_time?: number | string;
   extra?: KVMap;
   tags?: string[];
   error?: string;
@@ -501,4 +505,10 @@ export interface RunWithAnnotationQueueInfo extends BaseRun {
 
   /** The time this run was added to the queue. */
   added_at?: string;
+
+  /** The ISO 8601 formatted string representing the start time of the run. */
+  start_time: string;
+
+  /** The ISO 8601 formatted string representing the end time of the run, if available. */
+  end_time?: string;
 }
diff --git a/js/src/tests/client.int.test.ts b/js/src/tests/client.int.test.ts
index ddf160fa..4ce6952e 100644
--- a/js/src/tests/client.int.test.ts
+++ b/js/src/tests/client.int.test.ts
@@ -490,6 +490,7 @@ test.concurrent(
       id: runId,
       name: "foo",
       run_type: "llm",
+      start_time: new Date().toISOString(),
       inputs: { input: "hello world" },
       outputs: { output: "hi there" },
     };