diff --git a/packages/mui-material/src/Select/Select.test.js b/packages/mui-material/src/Select/Select.test.js
index e675791f7070d5..6e18710cdfe9b0 100644
--- a/packages/mui-material/src/Select/Select.test.js
+++ b/packages/mui-material/src/Select/Select.test.js
@@ -256,7 +256,8 @@ describe('<Select />', () => {
       await user.pointer({ keys: '[MouseLeft>]', target: trigger });
 
       await act(async () => {
-        await sleep(450);
+        // Well past the 400ms selected-item window; a tight margin flakes on slow CI.
+        await sleep(700);
       });
 
       await user.pointer({
@@ -283,7 +284,8 @@ describe('<Select />', () => {
       await user.pointer({ keys: '[MouseLeft>]', target: trigger });
 
       await act(async () => {
-        await sleep(250);
+        // Well past the 200ms drag window; a tight margin flakes on slow CI.
+        await sleep(400);
       });
       await user.pointer({
         keys: '[/MouseLeft]',
@@ -332,7 +334,8 @@ describe('<Select />', () => {
       await user.pointer({ keys: '[MouseLeft>]', target: trigger });
 
       await act(async () => {
-        await sleep(250);
+        // Well past the 200ms drag window; a tight margin flakes on slow CI.
+        await sleep(400);
       });
       await user.pointer({
         keys: '[/MouseLeft]',
diff --git a/packages/mui-material/src/Select/SelectInput.js b/packages/mui-material/src/Select/SelectInput.js
index 7c6c82f938dd93..ca6a28765f5676 100644
--- a/packages/mui-material/src/Select/SelectInput.js
+++ b/packages/mui-material/src/Select/SelectInput.js
@@ -383,14 +383,16 @@ const SelectInput = React.forwardRef(function SelectInput(props, ref) {
         selectionRef.current.allowUnselectedMouseUp = true;
       });
     } else {
+      // Both timers start from the mousedown. Chaining the selected timer inside the
+      // unselected callback would compound setTimeout jitter past the 400ms window.
       // mousedown -> move to unselected item -> mouseup should not select within 200ms.
       unselectedMouseUpTimer.start(UNSELECTED_MOUSE_UP_DELAY, () => {
         selectionRef.current.allowUnselectedMouseUp = true;
+      });
 
-        // mousedown -> mouseup on selected item should not select within 400ms.
-        selectedMouseUpTimer.start(UNSELECTED_MOUSE_UP_DELAY, () => {
-          selectionRef.current.allowSelectedMouseUp = true;
-        });
+      // mousedown -> mouseup on selected item should not select within 400ms.
+      selectedMouseUpTimer.start(SELECTED_MOUSE_UP_DELAY, () => {
+        selectionRef.current.allowSelectedMouseUp = true;
       });
     }
   };