diff --git a/src/grading-settings/deadline-section/utils.js b/src/grading-settings/deadline-section/utils.js
index 4b3e6249c..76308b802 100644
--- a/src/grading-settings/deadline-section/utils.js
+++ b/src/grading-settings/deadline-section/utils.js
@@ -17,7 +17,7 @@ export function formatTime(time) {
  * @returns {boolean} - returns `true` if `inputStr` is a valid time, else `false`.
  */
 export function timerValidation(inputStr, setShowSavePrompt, setIsError) {
-  const timePattern = /^(?:[01]\d|2[0-3]):[0-5]\d$/;
+  const timePattern = /^(?:\d{2,3}):[0-5]\d$/;
 
   const isValid = timePattern.test(inputStr);
   setShowSavePrompt(isValid);