Use one single definition of the date/time format in the config file

Change-Id: Ieccde4467405fbef85ab94a77cb339f72ce8ae36

src/main/java/com/googlesource/gerrit/plugins/messageoftheday/GetMessage.java

diff --git a/src/main/java/com/googlesource/gerrit/plugins/messageoftheday/GetMessage.java b/src/main/java/com/googlesource/gerrit/plugins/messageoftheday/GetMessage.java
index c04b9d9..5fbbed1 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/messageoftheday/GetMessage.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/messageoftheday/GetMessage.java
@@ -33,7 +33,7 @@
   private static final String KEY_STARTS_AT = "startsAt";
   private static final String KEY_EXPIRES_AT = "expiresAt";
 
-  private static final DateTimeFormatter DATE_FORMAT = DateTimeFormatter.ofPattern("yyyyMMdd:HHmm");
+  static final DateTimeFormatter DATE_FORMAT = DateTimeFormatter.ofPattern("yyyyMMdd:HHmm");
   private static final DateTimeFormatter REST_RESPONSE_FORMAT =
       DateTimeFormatter.ofPattern("MMM d, yyyy h:mm:ss a", Locale.ENGLISH);
 

src/main/java/com/googlesource/gerrit/plugins/messageoftheday/SetMessage.java

diff --git a/src/main/java/com/googlesource/gerrit/plugins/messageoftheday/SetMessage.java b/src/main/java/com/googlesource/gerrit/plugins/messageoftheday/SetMessage.java
index 3fc8898..ad36a09 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/messageoftheday/SetMessage.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/messageoftheday/SetMessage.java
@@ -14,6 +14,8 @@
 
 package com.googlesource.gerrit.plugins.messageoftheday;
 
+import static com.googlesource.gerrit.plugins.messageoftheday.GetMessage.DATE_FORMAT;
+
 import com.google.common.base.Strings;
 import com.google.common.flogger.FluentLogger;
 import com.google.gerrit.extensions.restapi.AuthException;
@@ -104,11 +106,7 @@
                 + INPUT_DATE_FORMAT_PATTERN
                 + "' format");
       }
-      cfg.setString(
-          SECTION_MESSAGE,
-          null,
-          KEY_EXPIRES_AT,
-          time.format(DateTimeFormatter.ofPattern("yyyyMMdd:HHmm")));
+      cfg.setString(SECTION_MESSAGE, null, KEY_EXPIRES_AT, time.format(DATE_FORMAT));
     } else {
       String expiredAt = cfg.getString(SECTION_MESSAGE, null, KEY_EXPIRES_AT);
       if (expiredAt == null) {