diff --git a/tools/jslint/check-all.js b/tools/jslint/check-all.js
index 54ac40594b..ceb871257c 100644
--- a/tools/jslint/check-all.js
+++ b/tools/jslint/check-all.js
@@ -114,6 +114,10 @@ var exceptions = {
 
     "Unexpected 'else' after 'return'." : function () {
         return true;
+    },
+
+    "Don't make functions within a loop." : function () {
+        return true;
     }
 };
 
diff --git a/zephyr/static/js/timerender.js b/zephyr/static/js/timerender.js
index 67a8b5a9a9..c9f13bc27b 100644
--- a/zephyr/static/js/timerender.js
+++ b/zephyr/static/js/timerender.js
@@ -2,16 +2,123 @@ var timerender = (function () {
 
 var exports = {};
 
+// If this is 5, then times from up to 5 days before the current
+// day will be formatted as weekday names:
+//
+//                     1/10 1/11 1/12
+// Sun  Mon  Tue  Wed  Thu  1/18 1/19
+//                     ^ today
+var MAX_AGE_FOR_WEEKDAY = 5;
+
+var next_timerender_id = 0;
+
+var set_to_start_of_day = function (time) {
+    return time.setMilliseconds(0).setSeconds(0).setMinutes(0).setHours(0);
+};
+
+function now() { return (new XDate()); }
+
+// Given an XDate object 'time', return a two-element list containing
+//   - a string for the current human-formatted version
+//   - a string like "2013-01-20" representing the day the format
+//     needs to change, or null if it will never need to change.
+function render_now(time) {
+    var start_of_today = set_to_start_of_day(now());
+    var start_of_other_day = set_to_start_of_day(time.clone());
+
+    // How many days old is 'time'? 0 = today, 1 = yesterday, 7 = a
+    // week ago, -1 = tomorrow, etc.
+
+    // Presumably the result of diffDays will be an integer in this
+    // case, but round it to be sure before comparing to an integer
+    // constant.
+    var days_old = Math.round(start_of_other_day.diffDays(start_of_today));
+
+    if (days_old >= 0 && days_old <= MAX_AGE_FOR_WEEKDAY)
+        // "\xa0" is U+00A0 NO-BREAK SPACE.
+        // Can't use &nbsp; as that represents the literal string "&nbsp;".
+        return [time.toString("ddd") + "\xa0" + time.toString("HH:mm"),
+                start_of_other_day.addDays(MAX_AGE_FOR_WEEKDAY+1)
+                .toString("yyyy-MM-dd")];
+    else {
+        // For now, if we get a message from tomorrow, we don't bother
+        // rewriting the timestamp when it gets to be tomorrow.
+        return [time.toString("MMM dd") + "\xa0\xa0" + time.toString("HH:mm"),
+                undefined];
+    }
+}
+
+// This table associates to each day (represented as a yyyy-MM-dd
+// string) a list of timestamps that need to be updated on that day.
+// Each timestamp is represented as a list of length 2:
+//   [id of the span element, XDate representing the time]
+
+// This is an efficient data structure because we only need to update
+// timestamps at the start of each day. If timestamp update times were
+// arbitrary, a priority queue would be more sensible.
+var update_table = {};
+
+// The day that elements are currently up-to-date with respect to.
+// Represented as an XDate with hour, minute, second, millisecond 0.
+var last_updated = set_to_start_of_day(now());
+
+function maybe_add_update_table_entry(update_date, id, time) {
+    if (update_date === undefined)
+        return;
+    if (update_table[update_date] === undefined)
+        update_table[update_date] = [];
+    update_table[update_date].push([id, time]);
+}
+
 // Given an XDate object 'time', return a DOM node that initially
 // displays the human-formatted time, and is updated automatically as
 // necessary (e.g. changing "Mon 11:21" to "Jan 14 11:21" after a week
 // or so).
 
-// (But for now it just returns a static node.)
-exports.render_time = function(time) {
-    // Wrap the text in a span because (oddly) a text node has no outerHTML attribute.
-    return $("<span />").text(time.toString("MMM dd") + "\xa0\xa0" + time.toString("HH:mm"));
+// (What's actually spliced into the message template is the contents
+// of this DOM node as HTML, so effectively a copy of the node. That's
+// okay since to update the time later we look up the node by its id.)
+exports.render_time = function (time) {
+    var id = "timerender" + next_timerender_id;
+    next_timerender_id++;
+    var rendered_now = render_now(time);
+    var node = $("<span />").attr('id', id).text(rendered_now[0]);
+    maybe_add_update_table_entry(rendered_now[1], id, time);
+    return node;
 };
 
+setInterval(function () {
+    var start_of_today = set_to_start_of_day(now());
+    var new_date;
+    // This loop won't do anything unless the day changed since the
+    // last time it ran.
+    for (new_date = last_updated.clone().addDays(1);
+         new_date <= start_of_today;
+         new_date.addDays(1)) {
+        var update_date = new_date.toString("yyyy-MM-dd");
+        if (update_table[update_date] !== undefined)
+        {
+            var to_process = update_table[update_date];
+            var i;
+            update_table[update_date] = [];
+            $.each(to_process, function (idx, elem) {
+                var id = elem[0];
+                var element = document.getElementById(id);
+                // The element might not exist any more (because it
+                // was in the zfilt table, or because we added
+                // messages above it and re-collapsed).
+                if (element !== null) {
+                    var time = elem[1];
+                    var new_rendered = render_now(time);
+                    $(document.getElementById(id)).text(new_rendered[0]);
+
+                    maybe_add_update_table_entry(new_rendered[1], id, time);
+                }
+            });
+        }
+    }
+    last_updated = start_of_today;
+}, 60 * 1000);
+
 return exports;
 }());