Didn't realize you were using calendar boxes.  Try this:
nw = new window("Test Dates", << modal(),
	text box("Monitoring & Trending"),
	hlistbox(
		panelbox("From Date",
			cal_start = calendar box(<< Show Time( 0 )),
		),
		panelbox("To Date",
			cal_end = calendar box(<< Show Time( 0 )),
		),
	),
	ok_button = button box("OK",
		startdate = cal_start << get date;
		enddate   = cal_end << get date;
	)
);
print(format(startdate, "ddMonyyyy" ), format(enddate, "ddMonyyyy" ));