Write data from Custom Object field to Contact custom field

Summary

Does anyone have an example of the above?

Content

I have a custom object group. Lets call it GroupObject. It has a number of objects within it. Lets call those.CObject1, CObject2 etc.and they each have fields.

In a CPM I want to write GroupObject.CObject1.time (time is one of the fields, it is not the current time) to:

contact_data->CustomFields->c->last_saved    a contact record custom field called last_saved.

Any example, for any part of this, would be greatly appreciated.