To get all records dated on the last day only.
If you do not specify time part, 00:00:00.000 is used.
BETWEEN '20080516' AND '20080517' would get you all records betweeen
20080516 00:00:00.000
20080516 00:00:00.003
...
20080516 23:59:59:997
20080517 00:00:00.000
If you use the suggested approach you will get desired records only.
20080516 00:00:00.000
20080516 00:00:00.003
...
20080516 23:59:59:997
N 56°04'39.16"
E 12°55'05.25"