Starting with version 18.1, it is possible to specify an auto-closing timeout using the XtraMessageBoxArgs.AutoCloseOptions.Delay and XtraMessageBoxArgs.AutoCloseOptions.ShowTimerOnDefaultButton properties:
C#XtraMessageBoxArgs args = new XtraMessageBoxArgs();
args.AutoCloseOptions.ShowTimerOnDefaultButton = true;
args.AutoCloseOptions.Delay = 5000;
args.Caption = "Default Text";
args.Text = "Continue?"
args.Buttons = new DialogResult[] { DialogResult.OK, DialogResult.Cancel };
XtraMessageBox.Show(args);