MM-61947 Run DND expiry job more often and round expiry time to match interval (#29938)

* MM-61947 Run DND expiry job more often and round expiry time to match interval

* Move comment to make it godoc-compatible

* Change truncateDNDEndTime to work with seconds

---------

Co-authored-by: Mattermost Build <build@mattermost.com>

server/channels/app/platform/status_test.go

@@ -6,6 +6,7 @@ package platform
 import (
 	"testing"
 
+	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 
 	"github.com/mattermost/mattermost/server/public/model"
@@ -37,3 +38,17 @@ func TestSaveStatus(t *testing.T) {
 		})
 	}
 }
+
+func TestTruncateDNDEndTime(t *testing.T) {
+	// 2025-Jan-20 at 17:13:32 GMT becomes 17:13:00
+	assert.Equal(t, int64(1737393180), truncateDNDEndTime(1737393212))
+
+	// 2025-Jan-20 at 17:13:00 GMT remains unchanged
+	assert.Equal(t, int64(1737393180), truncateDNDEndTime(1737393180))
+
+	// 2025-Jan-20 at 00:00:10 GMT becomes 00:00:00
+	assert.Equal(t, int64(1737331200), truncateDNDEndTime(1737331210))
+
+	// 2025-Jan-20 at 00:00:10 GMT remains unchanged
+	assert.Equal(t, int64(1737331200), truncateDNDEndTime(1737331200))
+}