diff --git a/src/streamlink/cache.py b/src/streamlink/cache.py
index a86aa0ce..9e55e4b1 100644
--- a/src/streamlink/cache.py
+++ b/src/streamlink/cache.py
@@ -38,7 +38,7 @@ class Cache:
         pruned = []
 
         for key, value in self._cache.items():
-            expires = value.get("expires", time())
+            expires = value.get("expires", now)
             if expires <= now:
                 pruned.append(key)
 
@@ -69,10 +69,13 @@ class Cache:
         if self.key_prefix:
             key = "{0}:{1}".format(self.key_prefix, key)
 
-        expires += time()
-
-        if expires_at:
-            expires = mktime(expires_at.timetuple())
+        if expires_at is None:
+            expires += time()
+        else:
+            try:
+                expires = mktime(expires_at.timetuple())
+            except OverflowError:
+                expires = 0
 
         self._cache[key] = dict(value=value, expires=expires)
         self._save()

diff --git a/tests/test_cache.py b/tests/test_cache.py
index 712d2c4f..895aabdd 100644
--- a/tests/test_cache.py
+++ b/tests/test_cache.py
@@ -55,6 +55,11 @@ class TestCache(unittest.TestCase):
         self.cache.set("value", 10, expires_at=datetime.datetime.now() + datetime.timedelta(seconds=20))
         self.assertEqual(10, self.cache.get("value"))
 
+    @patch("streamlink.cache.mktime", side_effect=OverflowError)
+    def test_expired_at_raise_overflowerror(self, mock):
+        self.cache.set("value", 10, expires_at=datetime.datetime.now())
+        self.assertEqual(None, self.cache.get("value"))
+
     def test_not_expired(self):
         self.cache.set("value", 10, expires=20)
         self.assertEqual(10, self.cache.get("value"))

mktime argument out of range when logging in to Crunchyroll after --crunchyroll-purge-credentials
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## Plugin Issue

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- [x] This is a plugin issue and I have read the contribution guidelines.
- [x] I am using the latest development version from the master branch.


### Description

Whenver I try to log in to Crunchyroll via streamlink I get an error.
<!-- Explain the plugin issue as thoroughly as you can. -->


### Reproduction steps / Explicit stream URLs to test

<!-- How can we reproduce this? Please note the exact steps below using the list format supplied. If you need more steps please add them. -->

1. I enter the command streamlink --crunchyroll-username=xxxx --crunchyroll-password=yyy --crunchyroll-purge-credentials https://www.crunchyroll.com/my/episode/to/watch best and I get it every time

### Log output

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```
[cli][debug] OS:         Windows 10
[cli][debug] Python:     3.6.6
[cli][debug] Streamlink: 1.7.0
[cli][debug] Requests(2.24.0), Socks(1.7.1), Websocket(0.57.0)
[cli][info] Found matching plugin crunchyroll for URL https://www.crunchyroll.com/jujutsu-kaisen/episode-10-idle-transfiguration-797874
[cli][debug] Plugin specific arguments:
[cli][debug]  --crunchyroll-username=kashiman290@gmail.com (username)
[cli][debug]  --crunchyroll-password=******** (password)
[cli][debug]  --crunchyroll-purge-credentials=True (purge_credentials)
[utils.l10n][debug] Language code: en_US
[plugin.crunchyroll][debug] Creating session with locale: en_US
[plugin.crunchyroll][debug] Session created with ID: 576c3d5d7a83d1dd18217343a6df37ff
[plugin.crunchyroll][debug] Attempting to login using username and password
[plugin.crunchyroll][debug] Credentials expire at: 1969-12-31 08:00:00
Traceback (most recent call last):
  File "runpy.py", line 193, in _run_module_as_main
  File "runpy.py", line 85, in _run_code
  File "C:\Program Files (x86)\Streamlink\bin\streamlink.exe\__main__.py", line 18, in <module>
  File "C:\Program Files (x86)\Streamlink\pkgs\streamlink_cli\main.py", line 1029, in main
    handle_url()
  File "C:\Program Files (x86)\Streamlink\pkgs\streamlink_cli\main.py", line 585, in handle_url
    streams = fetch_streams(plugin)
  File "C:\Program Files (x86)\Streamlink\pkgs\streamlink_cli\main.py", line 465, in fetch_streams
    sorting_excludes=args.stream_sorting_excludes)
  File "C:\Program Files (x86)\Streamlink\pkgs\streamlink\plugin\plugin.py", line 317, in streams
    ostreams = self._get_streams()
  File "C:\Program Files (x86)\Streamlink\pkgs\streamlink\plugins\crunchyroll.py", line 312, in _get_streams
    api = self._create_api()
  File "C:\Program Files (x86)\Streamlink\pkgs\streamlink\plugins\crunchyroll.py", line 384, in _create_api
    login = api.authenticate()
  File "C:\Program Files (x86)\Streamlink\pkgs\streamlink\plugins\crunchyroll.py", line 225, in authenticate
    self.cache.set("auth", self.auth, expires_at=data["expires"])
  File "C:\Program Files (x86)\Streamlink\pkgs\streamlink\cache.py", line 75, in set
    expires = mktime(expires_at.timetuple())
OverflowError: mktime argument out of range
```


### Additional comments, etc.



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tests/test_cache.py::TestCache::test_expired_at_raise_overflowerror
tests/test_cache.py::TestCache::test_create_directory tests/test_cache.py::TestCache::test_create_directory_fail tests/test_cache.py::TestCache::test_expired tests/test_cache.py::TestCache::test_expired_at_after tests/test_cache.py::TestCache::test_expired_at_before tests/test_cache.py::TestCache::test_get_all tests/test_cache.py::TestCache::test_get_all_prefix tests/test_cache.py::TestCache::test_get_all_prune tests/test_cache.py::TestCache::test_get_no_file tests/test_cache.py::TestCache::test_key_prefix tests/test_cache.py::TestCache::test_load_fail tests/test_cache.py::TestCache::test_not_expired tests/test_cache.py::TestCache::test_put_get tests/test_cache.py::TestCache::test_put_get_prefix