Strax is woken up by Madame Vastra and Jenny Flint, and is told that he had not died since they had used alien technology to heal his wounds. Jenny says that he had never truly passed away thanks to the resurrection technology and he had been in a state of unconsciousness for two days while the resurrection device healed him. He's angry about not having died. Vastra and Jenny then announce that the station is being evacuated, and they offer to take Strax with them back to London. Strax is hesitant and at first rudely refuses but then changes his mind and agrees to accompany them.
Since A Good Man Goes to War established that only River Song had the ability to take Vastra and Jenny back to their own time (the Doctor having departed in his TARDIS), the episode implies that it was at least two days before River was able to return them (as well as Amy Pond and Rory Williams) to their proper times.