unified datetime import style and fixed some import errors

wim.py

@@ -1,5 +1,5 @@
+import datetime
 import random
-from datetime import datetime, timedelta
 
 import streamlit as st
 import streamlit_authenticator as stauth
@@ -68,9 +68,9 @@
 if nav == "invullen":
     st.header("")
 
-    default_start = today - timedelta(days=today.weekday())  # Monday
-    default_end = default_start + timedelta(days=4)  # Friday
-    refresh_value = timedelta(days=7)
+    default_start = today - datetime.timedelta(days=today.weekday())  # Monday
+    default_end = default_start + datetime.timedelta(days=4)  # Friday
+    refresh_value = datetime.timedelta(days=7)
 
     date_range_string = date_range_picker(
         picker_type=PickerType.week,
@@ -145,8 +145,6 @@
         "wessel",
     ]
 
-    import datetime
-
     with tab1:
         current_week_number = datetime.datetime.now().isocalendar()[1]