Index: stamper/stamper.py
===================================================================
--- stamper/stamper.py	(revision 23)
+++ stamper/stamper.py	(revision 24)
@@ -61,5 +61,5 @@
         - %Y-%m-%d--%Y-%m-%d: Times recorded between two dates
 
-        - -%Y-%m-%d: Times recorded before a given date
+        - _%Y-%m-%d: Times recorded before a given date
 
         - +%Y-%m-%d: Times recorded after a given date
@@ -68,11 +68,11 @@
         """
         # First try the date filters, one by one
-        matches = ['%Y-%m-%d', '-%Y-%m-%d', '+%Y-%m-%d']
+        matches = ['%Y-%m-%d', '_%Y-%m-%d', '+%Y-%m-%d']
         for match in matches:
             try:
                 if '--' in stamp_filter:
                     filter_from, filter_to = stamp_filter.split('--')
-                    filter_from = datetime.strptime(stamp_filter, match)
-                    filter_to = datetime.strptime(stamp_filter, match)
+                    filter_from = datetime.strptime(filter_from, match)
+                    filter_to = datetime.strptime(filter_to, match)
                 else:
                     valid_filter = datetime.strptime(stamp_filter, match)