This 35 mm pinhole camera has an f/168 diaphragm. For calculating the time of exposure we will refer to the table of exposition values.
If we look at that table, we will see that the nearest value to this diaphragm is 1 second (or 2 seconds) and it appears inside a square. We must keep in mind that it is just an approximate value, for a normal sensitiveness of 125 ASA.
Finally it will be the practice and the experience that will determine in every case the most adequate exposure time.