(Answered) Total time required for changing structure/myomer type

[Saklad5]

On page 212 of the fourth printing of Campaign Operations, it is stated that changing the myomer or structure type of a 'Mech requires a base time of 360 minutes. If done using salvage or replacement rules, this would also require removing all components and armor currently in the old locations (that is, unless using FrankenMech rules, all locations) and adding them to the replacement locations.

Should the time required to do this be added to the "base time" of six hours, or should that be considered part of the Class F time multiplier?

[Xotl]

Each item involved in the refit, whether being added,
moved or removed, requires exactly one instance of its
standard replacement time

Nothing is "involved in the refit" unless you're specifically doing something to it.  You don't have to juggle the subsystems hypothetically required to allow the mounting of an item, or anything of that nature: you just have to find the right time amount for the time(s) you're actually working with and then apply the listed time multiplier.