Попробуйте минутный интервал 60?
$('#datetimepicker2').appendDtpicker({
todayButton: true,
step: 60,
closeOnSelected: true,
minuteInterval: 60,
minTime: "06:00",
maxTime: "23:59",
onSelect: function() {},
onInit: function(handler) {
var picker = handler.getPicker();
}
});