[DXCategory("Events")]
public virtual event EventHandler BeforePopup

<DXCategory("Events")>
Public Overridable Event BeforePopup As EventHandler

using DevExpress.XtraEditors.Popup;
using DevExpress.XtraEditors;
using DevExpress.Utils;
using System;

namespace DXApplication {
    public partial class Form1 : XtraForm {
        public Form1() {
            InitializeComponent();
            dateEdit1.BeforePopup += DateEdit1_BeforePopup;
        }

        void DateEdit1_BeforePopup(object sender, EventArgs e) {
            PopupDateEditForm popupForm = ((DateEdit)sender).GetPopupEditForm() as PopupDateEditForm;
            popupForm.Calendar.CalendarTimeEditing = DefaultBoolean.True;
        }
    }
}

Imports DevExpress.XtraEditors.Popup
Imports DevExpress.XtraEditors
Imports DevExpress.Utils
Imports System

Namespace DXApplication
    Public Partial Class Form1
        Inherits XtraForm

        Public Sub New()
            InitializeComponent()
            AddHandler dateEdit1.BeforePopup, AddressOf DateEdit1_BeforePopup
        End Sub

        Private Sub DateEdit1_BeforePopup(sender As Object, e As EventArgs)
            Dim popupForm As PopupDateEditForm = CType(CType(sender, DateEdit).GetPopupEditForm(), PopupDateEditForm)
            popupForm.Calendar.CalendarTimeEditing = DefaultBoolean.True
        End Sub
    End Class
End Namespace