When Adam and Eve, in Tangiers, get up to turn "the lovers," Eve leaves the flask and her left-hand glove on the bench. The next cut is a two-shot with Eve wearing the left-hand glove, but not the right. This is either a continuity error or it is an ironic gesture that the entire film to this point has been shot in reverse image as they are vampires without a reflection.
Dr. Watson makes a comment about the stethoscope around Adam's neck. The ear pieces are hanging on Adam's left side. In the shot in the hallway, the stethoscope is now hanging with the ear pieces on his right side.
Marlowe gives Eve and Adam the last of his "good stuff" - there is clearly very little left as they both tip the flask to drink the dregs. Cut to the couple in the street, building up the courage to go "a bit 15th century" on the lovers and they're taking decent drinks from the same flask and hardly lifting it - as if its pretty full.
There is no way to get from the USA (Detroit or Chicago) to Spain (Madrid) only flying at night. The flight will take at least 8 Hours and will cross 5 Timezones into the east towards sunrise. So night would progress at least 13 Hours.