I don't see how the OP has indicated that he intends to violate the ticket rules in this case. He is indicating that his onward flight to NBO would be leaving 20 hours after his arrival into LHR, which is within the 24 hour window for a connection (I don't think that the Oneworld Explorer has "must take the first available flight" rule as does the Oneworld Award). Am I missing something?

As for the OP's question, I am about 1 week ahaead of you w/r/t to my AONE5 ex/MRU. I made initial e-mail contact with BA in MRU on 1/18 and heard back from them on 1/23 with confirmed reservations on my first few flights (for which I gave them specific dates) and an active price quote. I submitted my credit card information to them via phone (with an e-mail follow-up) on 1/24 and am now awaiting e-mail confirmation of the ticketing with a ticket number. As others have done, I kept the routing simple so as to get an e-ticket and will expand on it once I have confirmation of ticketing.

How long does it usually take from payment to confirmation of ticketing?