BA's own website shows the BA275 as now due to land as LAS at 2332 with tonight's return BA274 showing a departure of 0135. The two-hour turnaround between landing and departure is about right. If they manage to make up any time at all I'd be surprised.
In spite of what @
sunshinebob exhorts, there's (little to) no chance of BA conjuring up another plane to operate tonight's BA274. I'd probably keep an eye on ba.com or EF or similar and probably aim to be at LAS in time for the inbound to arrive. Even that is probably a little too early.
I am not sure if The Club at LAS will remain open past its usual Midnight (T3 - E Gates) or 00.30 (T1 - D Gates) closing time if the BA flight is delayed?