Yes. They need be posted for only 24 hours.
Quoting my bug
Here are the relevant sections from CVC 22651:
(l) When a vehicle is illegally parked on a highway in violation
of a local ordinance forbidding standing or parking and the use of a
highway, or a portion thereof, is necessary for the cleaning, repair,
or construction of the highway, or for the installation of
underground utilities, and signs giving notice that the vehicle may
be removed are erected or placed at least 24 hours prior to the
removal by a local authority pursuant to the ordinance.
(m) Wherever the use of the highway, or a portion of the highway,
is authorized by a local authority for a purpose other than the
normal flow of traffic or for the movement of equipment, articles, or
structures of unusual size, and the parking of a vehicle would
prohibit or interfere with that use or movement, and signs giving
notice that the vehicle may be removed are erected or placed at least
24 hours prior to the removal by a local authority pursuant to the
(n) Whenever a vehicle is parked or left standing where local
authorities, by resolution or ordinance, have prohibited parking and
have authorized the removal of vehicles. A vehicle shall not be
removed unless signs are posted giving notice of the removal.