My question relates to the ongoing support of a hosted Wordpress site. In terms of hours, how much time needs to be budgeted for (per month) to update Wordpress etc with all the necessary patches etc...
Yeah I came across a few WP sites that had WSOD issues due to plugins and themes. The error logs should direct you in the right direction. Just be sure to make your weekly backups or after changes are made and you should be fine
A proper backup of the Wordpress site and MySQL DB including updating of plugins and re-testing functionality can take up to 3 hours depending on circumstances/how easy the upgrade went (didn't break functionality that should be working etc)
That's excluding time it takes to monitor up-time/404 errors/500 errors and if backups ran properly.
But if you're talking about purely clicking the "update" button and hoping for the best (crossing fingers nothing broke and sky diving without a backup), then 5 minutes.