I undertake website editing for a number of client websites, some using the Weebly, Wix or Free Webstore backends, some using bespoke Content Management Systems.
On occasion, when I build a website for a client, the client asks for training on how to update their own site - which I gladly provide.
More often than not, once the site is live, I am asked to maintain the site on behalf of the client.
I keep a timesheet of time spent on any given project and bill each client at the end of the month. NB If I only spend 5 minutes on something, I only charge for 5 minutes.