A service my company offers is similar to managed hosting where we help keep a server, Drupal, related modules, and backups up to date on behalf of clients who can't or don't want to do that in house, and typically this averages out to be about 30 to 90 min of work per site per month.
A client has asked me to manage their entire portfolio of 70 Drupal sites, all of which are part of a multisite architecture with site files on one server and DB on another.
I can't imagine that this is 70 hours of work, but I'm not familiar enough with multisite installs of this size to understand fully what this would entail.
To ensure that I estimate time correctly, what would I need to take into consideration when comparing management solutions for single server / single site installations as compared to the same number of sites in a multisite installation?