diff --git a/aleksis/apps/chronos/managers.py b/aleksis/apps/chronos/managers.py
index 7093cfec2c698370f6178eb9efbcd8b3d852018f..51d6ac522623ff6e068714c89d6cf84b77d5f034 100644
--- a/aleksis/apps/chronos/managers.py
+++ b/aleksis/apps/chronos/managers.py
@@ -12,7 +12,6 @@ from aleksis.apps.chronos.util.date import week_weekday_from_date
 from aleksis.core.models import Group, Person
 from aleksis.core.util.core_helpers import get_site_preferences
 
-from .models import LessonPeriod
 
 
 class TimetableType(Enum):
diff --git a/aleksis/apps/chronos/model_extensions.py b/aleksis/apps/chronos/model_extensions.py
index 6ad665587dfd1db2c7c4efb23cfa3ff3307e081a..ac9f9e790c8f504359cd4d6e52c5ea22dcb73730 100644
--- a/aleksis/apps/chronos/model_extensions.py
+++ b/aleksis/apps/chronos/model_extensions.py
@@ -10,13 +10,13 @@ from .managers import TimetableType
 from .models import Lesson, LessonPeriod
 
 
-@Person.property
+@Person.property_
 def is_teacher(self):
     """Check if the user has lessons as a teacher."""
     return self.lesson_periods_as_teacher.exists()
 
 
-@Person.property
+@Person.property_
 def timetable_type(self) -> Optional[TimetableType]:
     """Return which type of timetable this user has."""
     if self.is_teacher:
@@ -27,7 +27,7 @@ def timetable_type(self) -> Optional[TimetableType]:
         return None
 
 
-@Person.property
+@Person.property_
 def timetable_object(self) -> Optional[Union[Group, Person]]:
     """Return the object which has the user's timetable."""
     type_ = self.timetable_type
@@ -40,7 +40,7 @@ def timetable_object(self) -> Optional[Union[Group, Person]]:
         return None
 
 
-@Person.property
+@Person.property_
 def lessons_as_participant(self):
     """Return a `QuerySet` containing all `Lesson`s this person participates in (as student).
 
@@ -53,7 +53,7 @@ def lessons_as_participant(self):
     return Lesson.objects.filter(groups__members=self)
 
 
-@Person.property
+@Person.property_
 def lesson_periods_as_participant(self):
     """Return a `QuerySet` containing all `LessonPeriod`s this person participates in (as student).
 
@@ -66,7 +66,7 @@ def lesson_periods_as_participant(self):
     return LessonPeriod.objects.filter(lesson__groups__members=self)
 
 
-@Person.property
+@Person.property_
 def lesson_periods_as_teacher(self):
     """Return a `QuerySet` containing all `Lesson`s this person gives (as teacher).
 
diff --git a/aleksis/apps/chronos/models.py b/aleksis/apps/chronos/models.py
index 204e92ffb61bc49017b9bff7885a67319bb107f8..382a3e34c36c611ee6cf0b0ab4e4f8876b56181f 100644
--- a/aleksis/apps/chronos/models.py
+++ b/aleksis/apps/chronos/models.py
@@ -114,27 +114,27 @@ class TimePeriod(ExtensibleModel):
         return url_prev, url_next
 
     @classproperty
-    def period_min(self, cls) -> int:
+    def period_min(cls) -> int:
         return cls.objects.aggregate(period__min=Coalesce(Min("period"), 1)).get("period__min")
 
     @classproperty
-    def period_max(self, cls) -> int:
+    def period_max(cls) -> int:
         return cls.objects.aggregate(period__max=Coalesce(Max("period"), 7)).get("period__max")
 
     @classproperty
-    def time_min(self, cls) -> Optional[time]:
+    def time_min(cls) -> Optional[time]:
         return cls.objects.aggregate(Min("time_start")).get("time_start__min")
 
     @classproperty
-    def time_max(self, cls) -> Optional[time]:
+    def time_max(cls) -> Optional[time]:
         return cls.objects.aggregate(Max("time_end")).get("time_end__max")
 
     @classproperty
-    def weekday_min(self, cls) -> int:
+    def weekday_min(cls) -> int:
         return cls.objects.aggregate(weekday__min=Coalesce(Min("weekday"), 0)).get("weekday__min")
 
     @classproperty
-    def weekday_max(self, cls) -> int:
+    def weekday_max(cls) -> int:
         return cls.objects.aggregate(weekday__max=Coalesce(Max("weekday"), 6)).get("weekday__max")
 
     class Meta:
diff --git a/aleksis/apps/chronos/util/format.py b/aleksis/apps/chronos/util/format.py
index b5bf35c7816882330b3491b2957d2d84f307b3b8..ee9be702d00506f118974e533dd237f63825fb76 100644
--- a/aleksis/apps/chronos/util/format.py
+++ b/aleksis/apps/chronos/util/format.py
@@ -2,8 +2,6 @@ from datetime import date
 
 from django.utils.formats import date_format
 
-from ..models import TimePeriod
-
 
 def format_m2m(f, attr: str = "short_name") -> str:
     """Join a attribute of all elements of a ManyToManyField."""