A couple of heat cycles will help with stress relief of the parts and sometimes the builder.
The stresses built up by the cases need to be normalized and bolts checked.
How long it takes to achieve this is the question.
An old Winston Cup engine builder told me this
Fire it up for proof of life and listen for bad noises etc, Run it about 15 to 2000 RPM for about 2 minutes
Let it cool about an hour while checking everything.
Run it a second time , get it warm and run it at all RPMs changing it constantly. Run it about 10 min. after it gets warm.
Let it cool for an hour, check and adjust.
Fire it up, get it warm and see if it will run, If it stays together put it in the car and go fast.
The 1st run was with no load.
2nd run with about 10% load on the dyno.
3rd run put a load on it with the dyno.
If you want to do some power runs to get real numbers he liked to let it sit overnight then run it.
In the real world when you need a motor for the race tomorrow you build it in the motel bathtub and go race it.
He said they were banned from a few motel chains back in the 1970s for some reason.
My method for saws.
Fire it up, let it rattle everything around a few min.
Let cool.
Fire it tune it and run in wood about 1/2 tank , tune it then let cool.
Go and use it.
Check it often during the first 10 tanks then run it like a normal old chainsaw.