var getSPDayDiff = function(date) {
    return Math.round(Math.abs( ( new Date(1601,0,1).getTime() - date.getTime())/( 24*60*60*1000 ) ) );
}

var minDay = getSPDayDiff( new Date(2015,0,1) );
var maxDay = getSPDayDiff( new Date(2015,2,2) );

var $trDateTimeControl = $("input[id='"+ g_strDateTimeControlIDs["SPDateField1"] + "']").closest("tr");

var dateTimeHtml = $trDateTimeControl.find(".ms-dtinput:eq(1)").html();
dateTimeHtml = dateTimeHtml.replace("minjday=109207", "minjday="+minDay);
dateTimeHtml = dateTimeHtml.replace("maxjday=2666269", "maxjday="+maxDay);

$trDateTimeControl.find(".ms-dtinput:eq(1)").html( dateTimeHtml );