Schedule the timeout at absolute time.
Like timeout() but argument gives absolute time in the same clock system
as loop.time().
Please note: it is not POSIX time but a time with
undefined starting base, e.g. the time of the system power on.
>>> async with asyncio.timeout_at(loop.time() + 10):
... await long_running_task()
when - a deadline when timeout occurs or None to disable timeout logic
long_running_task() is interrupted by raising asyncio.CancelledError,
the top-most affected timeout() context manager converts CancelledError
into TimeoutError.