In the 1930s, the zeppelins LZ 127 Graf Zeppelin and LZ 129 Hindenburg made frequent transatlantic voyages. They had a top speed of around 85 mph, but I doubt they could manage that throughout the flight, especially with wind and storms. This leads to the interesting question of how long were the passengers stuck on a balloon with nothing but the vast expanse of sea underneath to look at?
The first transatlantic crossing by airship was made by the British R34 in July 1919, from East Fortune, Scotland to Mineola, New York, a journey which took 108 hours and 12 minutes. The R34 had not originally been designed as a passenger carrier, however, so this should not be seen as typical. The return journey to Norwich took 75 hours.
Regular passsenger service began with the Graf Zeppelin, which made its first crossing from Friedrichshafen to Lakehurst (New Jersey) in 1928. According to Airships.net, the journey took 111 hours and 44 minutes, but that is attributable to storms, damage, and a circuitous routing. It required 71 hours and 49 minutes for the return trip.
Another British airship, the R100, made the journey from Cardington, Bedfordshire to Montreal in 1930 in 78 hours, 49 minutes. The return took 57:56.
Graf Zeppelin's infamous sister, the Hindenburg, seems to have made better times. In 1936, its longest westbound trip from Frankfurt to Lakehurst was August 17–19, taking 90 hr 10 min, and the shortest came June 30-July 2 at 52:49. Eastbound, the longest journey was October 1–3 at 58:02, while the shortest was August 10–11 at 43:02.
Remember, the speed of an air journey is determined not only by the theoretical speed of the aircraft, but also by winds, as well as varying flight paths taken due to weather conditions. That is a big reason why eastbound journeys even in jet aircraft tend to take less time than their westbound counterparts.