The site operated for several years, although its exact period of operation is unknown.

But get to the last page and the stories jump abruptly from 2007 to 2004 - cutting out the exact period covered in the lawsuit.

The exact period when the city was built is not known.

The exact period of installation of this temple is not known.

The exact period when this migration happened is, however, not established.

This mounting technique most likely goes back hundreds of years; the exact period is unknown.

During the treatment, it is particularly important to note the starting time and to treat the hair for the exact period specified in the instructions.

Not even the pictures give a clue to the exact period covered by the events.

"I can't tell you the exact period of time, because it depends upon the special review process," he said.

I cannot tell the exact period that my trip will cover.