This example shows the problem using twisted, threads and freezetime

freeze_time_threads.py

from datetime import datetime
from functools import wraps

from freezegun import freeze_time

from twisted.internet import defer, reactor, threads


def tx_freeze_time(*ft_args, **ft_kwargs):
    def decorator(func):
        @wraps(func)
        @defer.inlineCallbacks
        def wrapper(*args, **kwargs):
            with freeze_time(*ft_args, **ft_kwargs):
                yield func(*args, **kwargs)
        return wrapper
    return decorator


def run_thread(func):
    return threads.deferToThread(func)


def internal_call():
    print("int", datetime.utcnow())
    return False


@freeze_time("2020-03-14 00:00:00")
@defer.inlineCallbacks
def external_call_buggy():
    print("ext", datetime.utcnow())
    result = yield run_thread(internal_call)
    defer.returnValue(result)


@tx_freeze_time("2020-03-14 00:00:00")
@defer.inlineCallbacks
def external_call():
    print("ext", datetime.utcnow())
    result = yield run_thread(internal_call)
    defer.returnValue(result)


@defer.inlineCallbacks
def main():
    print("Version with freeze_time: ")
    yield external_call_buggy()
    print("Version with tx_freeze_time: ")
    yield external_call()
    reactor.stop()


if __name__ == "__main__":
    reactor.callLater(0, main)
    reactor.run()

The output shows that using the regular freeze_time with decorator does not work, otherwise wrapping it a decorator using context manager just works.

$ python  freeze_time_threads.py 
Version with freeze_time:
('ext', FakeDatetime(2020, 3, 14, 0, 0))
('int', datetime.datetime(2020, 8, 24, 13, 2, 8, 732816))
Version with tx_freeze_time:
('ext', FakeDatetime(2020, 3, 14, 0, 0))
('int', FakeDatetime(2020, 3, 14, 0, 0))