Index: source/python/mods/checks.py
===================================================================
--- source/python/mods/checks.py	(revision 6f951ca0346aa6a2c3e11ee62df85214a290d838)
+++ source/python/mods/checks.py	(revision d4696e0eebad213794352c454f011ba6dc050ddc)
@@ -587,5 +587,5 @@
     Parameters
     ----------
-    basetime : str
+    basetime : int or str or None
         The time for a half day retrieval. The 12 hours upfront are to be
         retrieved.
@@ -593,11 +593,14 @@
     Return
     ------
-
-    '''
-    if basetime:
-        if int(basetime) != 0 and int(basetime) != 12:
+    basetime : int or None
+        The time for a half day retrieval. The 12 hours upfront are to be
+        retrieved.
+    '''
+    if basetime is not None:
+        basetime = int(basetime)
+        if basetime != 0 and basetime != 12:
             raise ValueError('ERROR: Basetime has an invalid value '
                              '-> {}'.format(str(basetime)))
-    return
+    return basetime
 
 def check_request(request, marsfile):
@@ -667,8 +670,8 @@
         try:
             if len(ftype) == 1 and ftype[0] != 'AN':
-                print('Use same field type as for the non-flux fields.')
+                print('... Use same field type as for the non-flux fields.')
                 acctype = ftype[0]
             elif len(ftype) > 1 and ftype[1] != 'AN':
-                print('Use old setting by using TYPE[1] for flux forecast!')
+                print('... Use old setting by using TYPE[1] for flux forecast!')
                 acctype = ftype[1]
         except:
@@ -681,8 +684,8 @@
 
 
-def check_acctime(acctime, acctype, purefc):
+def check_acctime(acctime, marsclass, purefc):
     '''Guarantees that the accumulation forecast times were set.
 
-    If it is not set, it is tried to set the value fore some of the
+    If it is not set, it tries to set the value for some of the
     most commonly used data sets. Otherwise it raises an error.
 
@@ -692,6 +695,6 @@
         The starting time from the accumulated forecasts.
 
-    acctype : str
-        The field type for the accumulated forecast fields.
+    marsclass : str
+        ECMWF data classification identifier.
 
     purefc : int
@@ -703,15 +706,16 @@
         The starting time from the accumulated forecasts.
     '''
+
     if not acctime:
         print('... Control parameter ACCTIME was not defined.')
         print('... Value will be set depending on field type:\n '
-              '\t\t EA=06/18\n\t\t EI/OD=00/12\n\t\t  EP=18')
-        if acctype.upper() == 'EA': # Era 5
+              '\t\t EA=06/18\n\t\t EI/OD=00/12\n\t\t EP=18')
+        if marsclass.upper() == 'EA': # Era 5
             acctime = '06/18'
-        elif acctype.upper() == 'EI': # Era-Interim
+        elif marsclass.upper() == 'EI': # Era-Interim
             acctime = '00/12'
-        elif acctype.upper() == 'EP': # CERA
+        elif marsclass.upper() == 'EP': # CERA
             acctime = '18'
-        elif acctype.upper() == 'OD' and not purefc: # On-demand operational
+        elif marsclass.upper() == 'OD' and not purefc: # On-demand
             acctime = '00/12'
         else:
@@ -720,5 +724,5 @@
     return acctime
 
-def check_accmaxstep(accmaxstep, acctype, purefc, maxstep):
+def check_accmaxstep(accmaxstep, marsclass, purefc, maxstep):
     '''Guarantees that the accumulation forecast step were set.
 
@@ -728,6 +732,6 @@
         The maximum forecast step for the accumulated forecast fields.
 
-    acctype : str
-        The field type for the accumulated forecast fields.
+    marsclass : str
+        ECMWF data classification identifier.
 
     purefc : int
@@ -746,9 +750,9 @@
         print('... Control parameter ACCMAXSTEP was not defined.')
         print('... Value will be set depending on field type/time: '
-              '\t\t EA/EI/OD=12\n\t\t  EP=24')
-        if acctype.upper() in ['EA', 'EI', 'OD'] and not purefc:
+              '\n\t\t EA/EI/OD=12\n\t\t EP=24')
+        if marsclass.upper() in ['EA', 'EI', 'OD'] and not purefc:
             # Era 5, Era-Interim, On-demand operational
             accmaxstep = '12'
-        elif acctype.upper() == 'EP': # CERA
+        elif marsclass.upper() == 'EP': # CERA
             accmaxstep = '18'
         elif purefc and accmaxstep != maxstep:
Index: source/python/mods/get_mars_data.py
===================================================================
--- source/python/mods/get_mars_data.py	(revision 6f951ca0346aa6a2c3e11ee62df85214a290d838)
+++ source/python/mods/get_mars_data.py	(revision d4696e0eebad213794352c454f011ba6dc050ddc)
@@ -252,9 +252,8 @@
     chunk = timedelta(days=int(c.date_chunk))
 
-    if c.basetime:
-        if c.basetime == '00':
-            start = start - timedelta(days=1)
-
-    if not c.purefc and fluxes:
+    if c.basetime == 0:
+        start = start - timedelta(days=1)
+
+    if not c.purefc and fluxes and not c.basetime == 0:
         start = start - timedelta(days=1)
         end = end + timedelta(days=1)
Index: source/python/mods/prepare_flexpart.py
===================================================================
--- source/python/mods/prepare_flexpart.py	(revision 6f951ca0346aa6a2c3e11ee62df85214a290d838)
+++ source/python/mods/prepare_flexpart.py	(revision d4696e0eebad213794352c454f011ba6dc050ddc)
@@ -152,5 +152,5 @@
     # since we need the 12 hours upfront
     # (the day before from 12 UTC to current day 00 UTC)
-    if c.basetime == '00':
+    if c.basetime == 0:
         start = start - datetime.timedelta(days=1)
 
Index: source/python/mods/tools.py
===================================================================
--- source/python/mods/tools.py	(revision 6f951ca0346aa6a2c3e11ee62df85214a290d838)
+++ source/python/mods/tools.py	(revision d4696e0eebad213794352c454f011ba6dc050ddc)
@@ -147,5 +147,5 @@
     parser.add_argument("--basetime", dest="basetime",
                         type=none_or_int, default=None,
-                        help="base such as 00 or 12 (for half day retrievals)")
+                        help="base such as 0 or 12 (for half day retrievals)")
     parser.add_argument("--step", dest="step",
                         type=none_or_str, default=None,
@@ -162,4 +162,8 @@
                         type=none_or_int, default=None,
                         help="debug mode - leave temporary files intact")
+    parser.add_argument("--oper", dest="oper",
+                        type=none_or_int, default=None,
+                        help="operational mode - prepares dates with \
+                        environment variables")
     parser.add_argument("--request", dest="request",
                         type=none_or_int, default=None,
