To what extent is local SEO a recurrent work?

Hello!

I am about to start out as a freelancer, offering web creation/dev services in Wordpress for independent contractors (lawyers, doctors, etc..).

I've noticed most of them find local SEO services extremely valuable, so I might include them in my post-sale monthly pack.

Many agencies offer monthly/recurrent local SEO services for independent contractors, at a cost of 100-200€/month.

My question is, does local SEO really require recurrent work? Or you just set everything up once and you're done? -what recurrent tasks does it require? -is there any way to automate them? -how time consuming is it? (Eg: how much time I should dedicate a month for each client)

Thanks!