asked to come in before shift, or warning will be given???

The staff received an email telling us that we are required to come in at
least 5 minutes before our shift starts to set up (turn on PCs, start necessary applications, etc) or else warnings will be given. Can
they really do that or do they need to actually schedule employees for that specific time to give warnings?

Additionally is there a website for "dummies" to reference California
labor laws, especially hours and shifts?

Thank you,
Mel Harland

Copy of email:
Team,
We have many mornings and afternoons where techs do not logon and are ready
at the start of their shifts.

I need everyone to get her 5 minutes before shifts to starts their PC's and
then be ready to take calls when your shift starts!

We will start to give out warnings if this is not done.
Thanks,
(Management person)