How to GetEvent by Date filter

[MinChanSike]

When I try to get event list filter by start date and end date, I got wrong results.
I got old event data response.
What I'm missing in code? Please take a look.

var startTime = DateTime.Now.Date.StartOfDay().ToUniversalTime();
var endTime = DateTime.Now.Date.EndOfDay().ToUniversalTime();

var filter = new Dictionary<Filters.Value, string>();
//filter.Add(Filters.Value.AckState, Event.AckStates.AckNeeded.ToString());
filter.Add(Filters.Value.StartTime, startTime.ToString());
filter.Add(Filters.Value.EndTime, endTime.ToString());
filter.Add(Filters.Value.Count, "50");
var results = _vxSystem.GetEvents(filter);