custom :class:`contextvars.Context` for the *callback* to run in.
The current context is used when no *context* is provided.
+ .. note::
+
+ For performance, callbacks scheduled with :meth:`loop.call_later`
+ may run up to one clock-resolution early (see
+ ``time.get_clock_info('monotonic').resolution``).
+
.. versionchanged:: 3.7
The *context* keyword-only parameter was added. See :pep:`567`
for more details.
An instance of :class:`asyncio.TimerHandle` is returned which can
be used to cancel the callback.
+ .. note::
+
+ For performance, callbacks scheduled with :meth:`loop.call_at`
+ may run up to one clock-resolution early (see
+ ``time.get_clock_info('monotonic').resolution``).
+
.. versionchanged:: 3.7
The *context* keyword-only parameter was added. See :pep:`567`
for more details.