diff --git a/extensions/vscode-api-tests/src/singlefolder-tests/notebook.test.ts b/extensions/vscode-api-tests/src/singlefolder-tests/notebook.test.ts
index 5498a89d6589143f73ad732d3883874977e8c406..1fce879547db792944ee81eb9b4da7c690e18867 100644
--- a/extensions/vscode-api-tests/src/singlefolder-tests/notebook.test.ts
+++ b/extensions/vscode-api-tests/src/singlefolder-tests/notebook.test.ts
@@ -122,7 +122,7 @@ suite('Notebook API tests', function () {
 							kind: vscode.NotebookCellKind.Code,
 							outputs: [],
 							metadata: { custom: { testCellMetadata: 123 } },
-							executionSummary: { startTime: 10, endTime: 20 }
+							executionSummary: { timing: { startTime: 10, endTime: 20 } }
 						},
 						{
 							value: 'test2',
@@ -1223,8 +1223,8 @@ suite('Notebook API tests', function () {
 		const cell = document.cellAt(0);
 
 		assert.strictEqual(cell.executionSummary?.success, undefined);
-		assert.strictEqual(cell.executionSummary?.startTime, 10);
-		assert.strictEqual(cell.executionSummary?.endTime, 20);
+		assert.strictEqual(cell.executionSummary?.timing?.startTime, 10);
+		assert.strictEqual(cell.executionSummary?.timing?.endTime, 20);
 
 	});
 
diff --git a/src/vs/vscode.d.ts b/src/vs/vscode.d.ts
index f56adfb89eddaec0b8d19cb0e3d31cc405c501f4..4fc5c0e4b966c1fc39e1cbe730fbc9301e677b64 100644
--- a/src/vs/vscode.d.ts
+++ b/src/vs/vscode.d.ts
@@ -11454,16 +11454,9 @@ declare module 'vscode' {
 		readonly success?: boolean;
 
 		/**
-		 * The unix timestamp at which execution started.
+		 * The times at which execution started and ended, as unix timestamps
 		 */
-		// @rob
-		//todo@API think about invalid state (no end, but start and vice versa)
-		readonly startTime?: number;
-
-		/**
-		 * The unix timestamp at which execution ended.
-		 */
-		readonly endTime?: number;
+		readonly timing?: { startTime: number, endTime: number };
 	}
 
 	/**
diff --git a/src/vs/workbench/api/common/extHostTypeConverters.ts b/src/vs/workbench/api/common/extHostTypeConverters.ts
index ba88ff0801cf8fd150fcb0975cfab3161ca16b89..9dc02f2235abc3a1056943d70e25e9c8a895625a 100644
--- a/src/vs/workbench/api/common/extHostTypeConverters.ts
+++ b/src/vs/workbench/api/common/extHostTypeConverters.ts
@@ -1418,8 +1418,7 @@ export namespace NotebookRange {
 export namespace NotebookCellExecutionSummary {
 	export function to(data: notebooks.NotebookCellInternalMetadata): vscode.NotebookCellExecutionSummary {
 		return {
-			startTime: data.runStartTime,
-			endTime: data.runEndTime,
+			timing: typeof data.runStartTime === 'number' && typeof data.runEndTime === 'number' ? { startTime: data.runStartTime, endTime: data.runEndTime } : undefined,
 			executionOrder: data.executionOrder,
 			success: data.lastRunSuccess
 		};
@@ -1428,8 +1427,8 @@ export namespace NotebookCellExecutionSummary {
 	export function from(data: vscode.NotebookCellExecutionSummary): Partial<notebooks.NotebookCellInternalMetadata> {
 		return {
 			lastRunSuccess: data.success,
-			runStartTime: data.startTime,
-			runEndTime: data.endTime,
+			runStartTime: data.timing?.startTime,
+			runEndTime: data.timing?.endTime,
 			executionOrder: data.executionOrder
 		};
 	}