Under FAA rules as an instructor you actually need to teach “something” in order to log PIC as an instructor.
You can’t just log ‘dual given’ without specifying what you taught and to whom.
So ‘straight and level flight 8.0 hrs’ doesn’t cut it.
There are numerous cases where the FAA went after instructors flying with each other and both logging PIC.
As in what were you teaching when both of you are instructors?!
So as a CFII can you fly with a time builder?
Yes, you can.
Just make it a meaningful flight and practice
things like VOR tracking and holds, instrument approaches, unusual attitude recovery etc etc
Keep a record of all training you provide and it’s legitimate PIC