diff --git a/slack_deleter/delete_batch.py b/slack_deleter/delete_batch.py
index de280bd..de25007 100644
--- a/slack_deleter/delete_batch.py
+++ b/slack_deleter/delete_batch.py
@@ -2,9 +2,7 @@
 import os
 import time
 
-import slack
-
-from .env import env_str
+from .utils import get_client, normalize_timestamp
 
 
 class BatchDeleter:
@@ -14,7 +12,7 @@ def cli(self, argv, prog=None):
             description='Delete messages from a list of timestamp IDs. Replies are also deleted.'
         )
         parser.add_argument('channel', help='Channel ID')
-        parser.add_argument('ts', nargs='+', help='Timestamps of messages')
+        parser.add_argument('ts', nargs='+', help='Timestamps of messages (format: 1586185432.000100 or 1586185432000100 or p1586185432000100)')
 
         args = parser.parse_args(argv)
         delete_count = self.run(args)
@@ -24,10 +22,11 @@ def cli(self, argv, prog=None):
             print('No messages found')
 
     def run(self, args):
-        client = slack.WebClient(token=env_str('SLACK_TOKEN'))
+        client = get_client()
         response = client.conversations_history(channel=args.channel, limit=1000)
+        ts = [normalize_timestamp(t) for t in args.ts]
         matches = [
-            msg for msg in response.data['messages'] if msg['ts'] in args.ts
+            msg for msg in response.data['messages'] if msg['ts'] in ts
         ]
 
         delete_count = 0
diff --git a/slack_deleter/delete_between.py b/slack_deleter/delete_between.py
index a84c869..e4978c4 100644
--- a/slack_deleter/delete_between.py
+++ b/slack_deleter/delete_between.py
@@ -2,9 +2,7 @@
 import os
 import time
 
-import slack
-
-from .env import env_str
+from .utils import get_client, normalize_timestamp
 
 
 class BetweenDeleter:
@@ -16,7 +14,7 @@ def cli(self, argv, prog=None):
                 'based on the parent timestamps.'
         )
         parser.add_argument('channel', help='Channel ID')
-        parser.add_argument('--from_ts', help='First timestamp to delete', default='0000000000.000000')
+        parser.add_argument('--from_ts', help='First timestamp to delete (format: 1586185432.000100 or 1586185432000100 or p1586185432000100)', default='0000000000.000000')
         parser.add_argument('--until_ts', help='Last timestamp to delete', default='9999999999.999999')
 
         args = parser.parse_args(argv)
@@ -27,10 +25,12 @@ def cli(self, argv, prog=None):
             print(f'No messages found')
 
     def run(self, args):
-        client = slack.WebClient(token=env_str('SLACK_TOKEN'))
+        client = get_client()
         response = client.conversations_history(channel=args.channel, limit=1000)
+        from_ts = normalize_timestamp(args.from_ts)
+        until_ts = normalize_timestamp(args.until_ts)
         matches = [
-            msg for msg in response.data['messages'] if args.from_ts <= msg['ts'] <= args.until_ts
+            msg for msg in response.data['messages'] if from_ts <= msg['ts'] <= until_ts
         ]
 
         delete_count = 0
diff --git a/slack_deleter/env.py b/slack_deleter/env.py
index 723ae46..0b9e249 100644
--- a/slack_deleter/env.py
+++ b/slack_deleter/env.py
@@ -6,11 +6,12 @@
 '''
 
 import os
+from pathlib import Path
 
 __all__ = ['BASE_DIR', 'abs_path', 'env_bool', 'env_str', 'env_list']
 
 
-BASE_DIR = os.path.dirname(__file__)
+ENV_PATH = Path(__file__).parent.parent / '.env'
 
 
 def env_setting(key, default):
@@ -18,11 +19,6 @@ def env_setting(key, default):
     return os.environ.get(key, default)
 
 
-def abs_path(*args):
-    '''Transforms relative path from `args` to absolute path, based on project root directory'''
-    return os.path.join(BASE_DIR, *args)
-
-
 def env_bool(name, default=False):
     '''
     Get a boolean value from environment variable.
@@ -75,7 +71,7 @@ def env_list(name, separator=',', default=None):
 
 
 def _load_env_file():
-    envfile = abs_path('.env')
+    envfile = ENV_PATH.resolve()
     if os.path.isfile(envfile):
         with open(envfile, 'r', encoding='utf-8') as fp:
             for line in fp:
@@ -87,3 +83,4 @@ def _load_env_file():
 
 
 _load_env_file()
+
diff --git a/slack_deleter/utils.py b/slack_deleter/utils.py
new file mode 100644
index 0000000..acca363
--- /dev/null
+++ b/slack_deleter/utils.py
@@ -0,0 +1,26 @@
+import time
+
+import slack
+
+from .env import env_str
+
+
+def get_client():
+    token = env_str('SLACK_TOKEN')
+    client = slack.WebClient(token=token)
+    return client
+
+def normalize_timestamp(ts):
+    """
+    Normalize Slack message timestamp.
+
+    Removes 'p' prefix and adds decimal separator if needed.
+    """
+    ts = str(ts)
+    if ts[0] == 'p':
+        ts = ts[1:]
+    if '.' not in ts:
+        ts = ts[:-6] + '.' + ts[-6:]
+
+    return ts
+