If you initialize the calendar with a date+time but only show the date editor, the time will be remain the same when dates are selected. Here's an example that ensures that you have the full days included at the endpoints:
Names Default To Here( 1 );
result = New Window( "Calendar Box Example",
<<Modal,
<<OnValidate(
fromDate = fromCal << Get Date();
toDate = toCal << Get Date();
1;
),
H List Box(
V List Box(
Text Box( "From:" ),
fromCal = Calendar Box( <<Date( Parse Date( "4/2/2002 12:00:00AM", "m/d/y h:m:s" ) ), <<Show Time( 0 ) )
),
V List Box(
Text Box( "To:" ),
toCal = Calendar Box( <<Date( Parse Date( "10/14/2003 11:59:59PM", "m/d/y h:m:s" ) ), <<Show Time( 0 ) )
),
)
);
If( result["Button"] == 1,
New Window( "results",
V List Box(
Text Box( "From: " || Format( fromDate, "M/D/Y h:m:s" ) ),
Text Box( "To: " || Format( toDate, "M/D/Y h:m:s" ) )
)
)
);