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Is there a way to drop instances on to an existing time line and have it overwrite, so as not to disturb the timing of the layer after the insertion?

The way I do this is to select the instances and watch the number of frames at the top of the Layer Panel to know the exact count.
Hit Copy and then select the same number of frames where you want to place these and Paste.

Thanks Paul. That's a good work around, but a bit fiddly. If you copy a section which is 28 frames, you have to count those frames and then carefully select exactly 28 frames on the incoming layer. Not so practical, but at least it can be done. It's surprising to me that there is not an easy and simple way to overwrite rather than insert.

By the way, while I have your attention! When I insert, of course all the instances renumber. Is there a way to create an instance, have it be automatically given a name or number and that name be fixed to it? Or does every instance have to be named manually one at a time? Also, in terms of copying and pasting an instance so that it is not a copy, but a reuse of the same instance, is that process any different in version 11?

Wait a minute; I don't know what I was thinking when I told you about counting frames. You just highlight your frames, drag them anywhere, drop, and choose "Copy". You can do the same with renamed frames and yes, the new names travel with the instances.
EDIT: I didn't answer your entire question: If you want to rename a sequence of instances, select them and hit the "Auto" button to the right of the green one.

is that process any different in version 11?

in the version 11, if you right click on the timeline, you have some options to rename all the instances of a layer.