Is this a same day arrival/departure or do you depart the next day?

I get the feeling from your question that you are not familiar with LHR and with that, that you may be thinking of spending your time in one of the BA T5 Lounges but please correct me if I'm reading this the wrong way.

If your BA departure to DUS is the next day, you will have to find alternative arrangements to staying in the lounge as T5 closes for the night.

One of the resident experts will no doubt be along to advise you better if this is the case.

If my thinking is going off on a tangent then please ignore .

Safe & Happy Travels

S

Edit To Add: Missed the crucial (overnight) bit you put in the OP. You will have to find alternative accomodation overnight but will have access to the T5 GC Lounges (North, South or T5B) unless you have OWE status allowing you access to the T5 FLounge on the day of departure.