He lay in a stupor for some unknown length of time.

The entire document is of unknown length, probably over 1,000 pages.

But we're an unknown length away from that.

The name has served my small need for more than twenty years of a life of unknown length.

That development could lead to delays of unknown length, he said.

It has a dirt runway of an unknown length, as well as a small terminal.

The "prisoner's dilemma"; which way to turn in a tunnel of unknown length and only one end open?

He had no fancy for a drive of unknown length on a cold night in February.

Impatience was a vice when beginning a journey of unknown length.

When I start remembering again there will be a blank of unknown length.