diff --git a/aosstower/level_a0/nc.py b/aosstower/level_a0/nc.py
index 774f29b474e9274973449821d80eb6428c4c195e..91e75227d4ab4fcb1bf1ce85ca4fc308b391aba2 100644
--- a/aosstower/level_a0/nc.py
+++ b/aosstower/level_a0/nc.py
@@ -266,7 +266,10 @@ def createMultiple(filenames, outputFilenames, zlib, chunkSize):
 
 def _dt_convert(datetime_str):
     #parse datetime string, return datetime object
-    return dt.strptime(datetime_str, '%Y-%m-%dT%H:%M:%S')
+    try: 
+        return dt.strptime(datetime_str, '%Y-%m-%dT%H:%M:%S')
+    except:
+        return dt.strptime(datetime_str, '%Y-%m-%d')
  
 def main():
     import argparse
@@ -280,8 +283,11 @@ def main():
                          help='each occurrence increases verbosity 1 level through ERROR-WARNING-INFO-DEBUG (default INFO)')
 
     #argparse start and end times
-    parser.add_argument('-s', '--start-time', type=_dt_convert, help="Start time of massive netcdf file")
-    parser.add_argument('-e', '--end-time', type=_dt_convert, help='End time of massive netcdf file')
+    parser.add_argument('-s', '--start-time', type=_dt_convert, 
+        help="Start time of massive netcdf file, if only -s is given, a netcdf file for only that day is given" + 
+        ". Formats allowed: \'YYYY-MM-DDTHH:MM:SS\', \'YYYY-MM-DD\'")
+    parser.add_argument('-e', '--end-time', type=_dt_convert, help='End time of massive netcdf file. Formats allowed:' +
+        "\'YYYY-MM-DDTHH:MM:SS\', \'YYYY-MM-DD\'")
     parser.add_argument('-cs', '--chunk-size', type=int, help='chunk Size for the netCDF file')
     parser.add_argument('-z', '--zlib', action='store_true', help='compress netCDF file with zlib')
 
@@ -302,8 +308,14 @@ def main():
         if(result == False):
             raise IOError('An empty ASCII file was found')
 
-    elif(args.start_time or args.end_time):
-        print('USAGE: start time and end time must both be specified or not specified')
+    elif(args.start_time):
+        end_time = args.start_time.replace(hour=23, minute=59, second=59)
+        result = createGiantNetCDF(args.start_time, end_time, args.input_files, args.output[0], args.zlib, args.chunk_size)
+        if(result == False):
+            raise IOError('An empty ASCII file was found')
+
+    elif(args.end_time):
+        print('USAGE: start time must be specified when end time is specified')
 
     else:
         createMultiple(args.input_files, args.output, args.zlib, args.chunk_size)