No, I don't think it should matter at all - will only occur at specific time but I don't think there are any requirements
OK started new game and went straight to Carla on first Tuesday night, no rumpy pumpy so there is a criteria, but it must be one I've always done without even noticing;
I always start with the quest "The terrible secret of Fina Ironheart" which is assigned (sort of) by Carla, that might be it. Otherwise it's something like chatting to her, I'll let you know if I find out more but ...
Right did it again, in bed with Carla on first Tuesday, things done ...
Chat to Carla Monday moring, get "The terrible secret of Fina Ironheart" quest;
Completed quest on Monday evening;
Chatted to Carla on Tuesday evening and chose flirt option
Visited her bedroom on Tuesday evening and had sex
And from there on sex whenever