diff --git a/models/problem.js b/models/problem.js
index e89eccb..9014e25 100644
--- a/models/problem.js
+++ b/models/problem.js
@@ -244,17 +244,14 @@ let model = db.define('problem', {
   file_io_input_name: { type: Sequelize.TEXT },
   file_io_output_name: { type: Sequelize.TEXT },
 
-  create_time: { type: Sequelize.DATE },
-  last_update: { type: Sequelize.DATE },
+  publicize_time: { type: Sequelize.DATE },
 
   type: {
     type: Sequelize.ENUM,
     values: ['traditional', 'submit-answer', 'interaction']
   }
 }, {
-    timestamps: true,
-    createdAt: 'create_time',
-    updatedAt: 'last_update',
+    timestamps: false,
     tableName: 'problem',
     indexes: [
       {
@@ -264,10 +261,7 @@ let model = db.define('problem', {
         fields: ['user_id'],
       },
       {
-        fields: ['create_time'],
-      },
-      {
-        fields: ['last_update'],
+        fields: ['publicize_time'],
       },
     ]
   });
diff --git a/modules/index.js b/modules/index.js
index 023686e..73741a4 100644
--- a/modules/index.js
+++ b/modules/index.js
@@ -47,10 +47,10 @@ app.get('/', async (req, res) => {
 
     let contests = await Contest.query([1, 5], { is_public: true }, [['start_time', 'desc']]);
 
-    let problems = (await Problem.query([1, 5], { is_public: true }, [['last_update', 'desc']])).map(problem => ({
+    let problems = (await Problem.query([1, 5], { is_public: true }, [['publicize_time', 'desc']])).map(problem => ({
       id: problem.id,
       title: problem.title,
-      time: timeAgo.format(new Date(problem.last_update)),
+      time: timeAgo.format(new Date(problem.publicize_time)),
     }));
 
     res.render('index', {
diff --git a/modules/problem.js b/modules/problem.js
index f30da2d..dcc990d 100644
--- a/modules/problem.js
+++ b/modules/problem.js
@@ -581,6 +581,7 @@ async function setPublic(req, res, is_public) {
 
     problem.is_public = is_public;
     problem.publicizer_id = res.locals.user.id;
+    problem.publicize_time = new Date();
     await problem.save();
 
     JudgeState.model.update(