I ran a quick test based on one of the samples and can't repro the issue. In my test code (see below) features with a date of 1/1/2012 are displaying for the last set of tics.
<!DOCTYPE html>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<meta http-equiv="X-UA-Compatible" content="IE=7,IE=9">
<!--The viewport meta tag is used to improve the presentation and behavior of the samples
on iOS devices-->
<meta name="viewport" content="initial-scale=1, maximum-scale=1,user-scalable=no">
<title>Demo</title>
<link rel="stylesheet" href="http://serverapi.arcgisonline.com/jsapi/arcgis/3.3/js/dojo/dijit/themes/claro/claro.css">
<link rel="stylesheet" href="http://serverapi.arcgisonline.com/jsapi/arcgis/3.3/js/esri/css/esri.css">
<script>var dojoConfig = { parseOnLoad: true }; </script>
<script src="http://serverapi.arcgisonline.com/jsapi/arcgis/3.3/"></script>
<script language="Javascript">
dojo.require("esri.map");
dojo.require("esri.dijit.TimeSlider");
dojo.require("esri.layers.FeatureLayer");
var map;
function init() {
var startExtent = new esri.geometry.Extent({"xmin":-13740877.445278011,"ymin":5653763.518179012,"xmax":-13588003.3887076,"ymax":5745487.95212126,"spatialReference":{"wkid":102100}});
map = new esri.Map("map", {
basemap: "streets",
extent: startExtent
});
var infoTemplate = new esri.InfoTemplate("Attributes", "${*}");
var fl = new esri.layers.FeatureLayer("http://cgisagsec2.portlandoregon.gov/arcgis/rest/services/BPS/solar_pdx/MapServer/0",{
mode: esri.layers.FeatureLayer.MODE_SNAPSHOT,
infoTemplate: infoTemplate
});
map.addLayers([fl]);
dojo.connect(map, "onLayersAddResult", initSlider);
}
function initSlider() {
var timeSlider = new esri.dijit.TimeSlider({
style: "width: 1000px;"
}, dojo.byId("timeSliderDiv"));
map.setTimeSlider(timeSlider);
var timeExtent = new esri.TimeExtent();
timeExtent.startTime = new Date("1/1/2009 UTC");
timeExtent.endTime = new Date("1/31/2012 UTC");
timeSlider.setThumbCount(2);
timeSlider.createTimeStopsByTimeInterval(timeExtent,1,'esriTimeUnitsMonths');
timeSlider.setThumbIndexes([0,1]);
timeSlider.setThumbMovingRate(2000);
timeSlider.startup();
}
dojo.ready(init);
</script>
</head>
<body class="claro">
<div id="map" style="width:1000px; height:600px; border:1px solid #000;"></div>
<div id="timeSliderDiv"></div>
</body>
</html>