Three...
Conduct no more than three open water scuba training dives in a single day,after completion of the Open Water Diver course dives.
night or combination thereof. When conducting a third dive for Open Water
Diver course students, the maximum depth of the third dive must not exceed
12 metres/40 feet. This applies to an Adventure Dive conducted as a third dive
Steve - I stand corrected. A max 12m depth for the third dive would stop you from doing the deep spec in a day & most wrecks though