Bag drop - how soon?
 

We are flying from ABZ to LHR then LHR to JNB next Tuesday. We booked the trip on the BA holiday Sale in December 2018, we got a good price for the flights and car hire. However, we had to book the ABZ to LHR as a seperate ticket as the "special" price was from LHR only. We are aware that we will have to collect our checked luggage in LHR and recheck it on to JNB. We have allowed lots of time between landing at LHR and departing for JNB incase of delays, especially at this time of year.
My question is, how long before our departure to JNB can we drop our checked bags off, pass security and go to the lounge ( we are flying CW, no status just Blues).

Any time from 5am on the day of departure.