Absolute exposure time

We need to make a philosophical choise about absolute exposure time.
In operation, we don't care too much about this, because exposures are much longer.

However, during our current test, exposure is only few seconds.
The opening of the shutters last about 0.39s
The closing of the shutters last about 0.38s

If we open and close right away, let's call that a 0 sec exposure, here is what the detector actually see in terms of exposure time:

What I would propose, it's to choose the least bad solution :

exptime = (shutter_opening_time+shutter_closing_time)/2 + time_shutters_fully_open
for that "0 sec" exposure above it would give a 0.385 absolute exposure time.

Anyhow, I think that's important enough so I can't be the only one to decide.
The sooner the better.

Thanks.