I bought separate flight tickets, arriving at LHR T4 (QR flight) at 06:30 and taking a flight from LHR (T5) > NCL (BA flight) which now departs at 16:55 after they just cancelled the earlier flight. I am aware there is an earlier flight departing at 09:20 (but I booked a later flight, originally at about 1pm, in case of delays with the flight / border control / security), and I am also aware that I can change to an earlier flight (same route) on the day itself for free if there's availability.

With operational issues at LHR now extending into winter (I'm flying in October), I wonder what's the estimated time to transfer from T4 to T5 assuming I do not tag my luggage through and I will collect my luggage at T4, then check in for my BA flight at T5? The MCT suggested on HAL website is 105 minutes but I think that's for airside transit. With almost 3 hours of total transit time, is there enough time for me to collect my luggage at T4, go to T5 and check in for my next flight within 2 hours of landing?

I'm just thinking if this is not feasible, would it be better to have my luggage tagged to NCL so I'll just go for a day trip into London city itself without having to worry about my luggage for about 10 hours? Would this be more likely to result in lost luggage compared to me collecting it at LHR T4?