diff --git a/packages/delegation-toolkit/src/experimental/erc7715GrantPermissionsAction.ts b/packages/delegation-toolkit/src/experimental/erc7715GrantPermissionsAction.ts
index 6e99503c..cb878829 100644
--- a/packages/delegation-toolkit/src/experimental/erc7715GrantPermissionsAction.ts
+++ b/packages/delegation-toolkit/src/experimental/erc7715GrantPermissionsAction.ts
@@ -28,7 +28,7 @@ export type NativeTokenStreamPermission = Permission & {
   data: {
     initialAmount?: bigint;
     amountPerSecond: bigint;
-    startTime: number;
+    startTime?: number;
     maxAmount?: number;
     justification: string;
   };
@@ -392,10 +392,6 @@ function formatNativeTokenStreamPermission(
     permission.data.justification,
     'Invalid parameters: justification is required',
   );
-  assertIsDefined(
-    permission.data.startTime,
-    'Invalid parameters: startTime is required',
-  );
 
   const isInitialAmountSpecified =
     permission.data.initialAmount !== undefined &&
@@ -405,6 +401,10 @@ function formatNativeTokenStreamPermission(
     permission.data.maxAmount !== undefined &&
     permission.data.maxAmount !== null;
 
+  const isStartTimeSpecified =
+    permission.data.startTime !== undefined &&
+    permission.data.startTime !== null;
+
   const optionalFields = {
     ...(isInitialAmountSpecified && {
       initialAmount: toHexOrThrow(permission.data.initialAmount),
@@ -412,6 +412,9 @@ function formatNativeTokenStreamPermission(
     ...(isMaxAmountSpecified && {
       maxAmount: toHexOrThrow(permission.data.maxAmount),
     }),
+    ...(isStartTimeSpecified && {
+      startTime: Number(permission.data.startTime),
+    }),
   };
 
   return {
@@ -421,7 +424,6 @@ function formatNativeTokenStreamPermission(
         permission.data.amountPerSecond,
         'Invalid parameters: amountPerSecond is required',
       ),
-      startTime: Number(permission.data.startTime),
       justification: permission.data.justification,
       ...optionalFields,
     },
diff --git a/packages/delegation-toolkit/test/experimental/erc7715GrantPermissionsAction.test.ts b/packages/delegation-toolkit/test/experimental/erc7715GrantPermissionsAction.test.ts
index cec5fc58..28d544f0 100644
--- a/packages/delegation-toolkit/test/experimental/erc7715GrantPermissionsAction.test.ts
+++ b/packages/delegation-toolkit/test/experimental/erc7715GrantPermissionsAction.test.ts
@@ -137,31 +137,6 @@ describe('erc7715GrantPermissionsAction', () => {
       ).rejects.toThrow('Invalid parameters: amountPerSecond is required');
     });
 
-    it('should throw an error when startTime is undefined', async () => {
-      const parameters = [
-        {
-          chainId: 31337,
-          address: bob.address,
-          expiry: 1234567890,
-          permission: {
-            type: 'native-token-stream',
-            data: {
-              amountPerSecond: '0x1',
-              maxAmount: '0x2',
-              startTime: undefined,
-              justification: 'Test justification',
-            },
-          },
-          isAdjustmentAllowed: false,
-          signer: { type: 'account', data: { address: alice.address } },
-        },
-      ];
-
-      await expect(
-        erc7715GrantPermissionsAction(mockClient, parameters),
-      ).rejects.toThrow('Invalid parameters: startTime is required');
-    });
-
     it('should throw an error when justification is undefined', async () => {
       const parameters = [
         {