Exceptions:
Nationals of above listed countries do NOT require an airport transit visa if
- they hold a valid visa for the United States of America, or
- they hold a used valid or expired visa issued by the US, return from the US and travel to a non-Schengen Member State within 24 hours after the visa expired.
The above is from German consulate in USA. The statement that travel should be within 24 hrs of visa expiry make it clear that transit visa is needed after 24 hrs of H1B visa expiry
See Airport Transit in Germany and Airport Transit Country List (PDF), which is the source of the quotation above.
