I am trying to improve the efficiency of this code so that it runs as quickly as possible. Does anyone have any suggestions on how I can speed this up?

// Grab the "Event" document type
DocumentType dt = DocumentType.GetByAlias("Event");

// Grab all published events
var allevents = Document.getContentOfContentType(dt).Where(e => !e.IsTrashed &&
  !string.IsNullOrEmpty(e.getProperty("startDateTime").Value.ToString()) &&
  !string.IsNullOrEmpty(e.getProperty("finishDateTime").Value.ToString())
).ToList();

// Now check to see if we need to show only those related to a certain page
if (nodeId != "0")
{
  DocumentType dtPage = DocumentType.GetByAlias("Page");
  var descendants = Document.getContentOfContentType(dtPage).Where(p => !p.IsTrashed &&
  p.Path != null &&
  p.Path.Split(',').Any(i => i == nodeId) &&
  p.Id != null &&
  p.Id.ToString() != nodeId).Select(p => p.Id.ToString()).ToList<string>();
  descendants.Add(nodeId);

  allevents = allevents.Where(e => descendants.Intersect(e.getProperty("relatedPages").Value.ToString().Split(',')).Count() > 0).ToList();
}

// Filter by those in the current date range
var exactmatches = allevents.Where(e => (DateTime.Parse(e.getProperty("startDateTime").Value.ToString()) >= start && DateTime.Parse(e.getProperty("startDateTime").Value.ToString()) <= end)
                ||
                (DateTime.Parse(e.getProperty("finishDateTime").Value.ToString()) >= start && DateTime.Parse(e.getProperty("finishDateTime").Value.ToString()) <= end)
).ToList();