Although this doesn't help you with Stockholm, for others looking to complete the challenge, the consecutive night groupings (i.e., if you did Monday - Tuesday and a Tuesday-Wednesday stays, that would end up being combined into 1 stay) is per property.

Staying the same night at two separate Marriott properties on the same night would count as two separate stays, for an accelerator (i.e., Monday - Tuesday at a Marriott and the same Monday-Tuesday at a Courtyard).