diff --git a/lib/nexrad/vtec.py b/lib/nexrad/vtec.py
index 343f26e..7153f23 100644
--- a/lib/nexrad/vtec.py
+++ b/lib/nexrad/vtec.py
@@ -63,6 +63,8 @@ class VTECEventType(enum.StrEnum):
     EXPERIMENTAL_VTEC = 'X'
 
 class VTECBaseEvent():
+    __slots__ = 'timestamp_start', 'timestamp_end',
+
     timestamp_start: datetime.datetime
     timestamp_end:   datetime.datetime
 
@@ -71,20 +73,17 @@ class VTECBaseEvent():
         self.timestamp_end   = None
 
     def parse_timestamps(self, text_start: str, text_end: str):
-        start = parse_timestamp(text_start)
-        end   = parse_timestamp(text_end)
+        if not is_timestamp_zero(text_start):
+            self.timestamp_start = parse_timestamp(text_start)
 
-        if is_timestamp_zero(text_start) and not is_timestamp_zero(text_end):
-            self.timestamp_start = end
-            self.timestamp_end   = end
-        elif not is_timestamp_zero(text_start) and is_timestamp_zero(text_end):
-            self.timestamp_start = start
-            self.timestamp_end   = start
-        else:
-            self.timestamp_start = start
-            self.timestamp_end   = end
+        if not is_timestamp_zero(text_end):
+            self.timestamp_end = parse_timestamp(text_end)
 
 class VTECEvent(VTECBaseEvent):
+    __slots__ = (
+        'typeof', 'actions', 'wfo', 'phenom', 'sig', 'etn'
+    )
+
     typeof:  str
     actions: str
     wfo:     str
@@ -92,9 +91,6 @@ class VTECEvent(VTECBaseEvent):
     sig:     str
     etn:     int
 
-    timestamp_start: datetime.datetime
-    timestamp_end:   datetime.datetime
-
     @staticmethod
     def parse(text: str) -> Self:
         match = RE_PHENOM.match(text)
@@ -116,16 +112,13 @@ class VTECEvent(VTECBaseEvent):
 
 class VTECHydroEvent(VTECBaseEvent):
     __slots__ = (
-        'severity', 'cause', 'record', 'timestamp_start', 'timestamp_end'
+        'severity', 'cause', 'record'
     )
 
     severity: str
     cause:    str
     record:   str
 
-    timestamp_start: datetime.datetime
-    timestamp_end:   datetime.datetime
-
     @staticmethod
     def parse(text: str) -> Self:
         match = RE_HYDRO.match(text)