Now the requirement is clear, thanks.
There is no such built-in functionality to change a format, but it's possible to override it.
See the comment in the JavaScript code.
Example
<%@ Page Language="C#" %>
<%@ Register Assembly="Ext.Net" Namespace="Ext.Net" TagPrefix="ext" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title>Ext.NET Example</title>
<ext:ResourcePlaceHolder runat="server" Mode="ScriptFiles" />
<script type="text/javascript">
Ext.calendar.DayBodyTemplate.override({
applyTemplate : function (o) {
this.today = new Date().clearTime();
this.dayCount = this.dayCount || 1;
var i,
days = [],
dt = o.viewStart.clone(),
times;
for(i = 0; i < this.dayCount; i++) {
days[i] = dt.add(Date.DAY, i);
}
times = [];
dt = new Date().clearTime();
for(i = 0; i < 24; i++) {
times.push(dt.format('G')); //the default value is 'ga'.
//Change to a respective format, see the link below.
dt = dt.add(Date.HOUR, 1);
}
return Ext.calendar.DayBodyTemplate.superclass.applyTemplate.call(this, {
days : days,
dayCount : days.length,
times : times
});
}
});
</script>
</head>
<body>
<form runat="server">
<ext:ResourceManager runat="server" />
<ext:Viewport runat="server" Layout="fit">
<Items>
<ext:CalendarPanel ID="CalendarPanel1" runat="server">
<EventStore runat="server" />
</ext:CalendarPanel>
</Items>
</ext:Viewport>
</form>
</body>
</html>
See also
http://docs.sencha.com/ext-js/3-4/#!/api/Date