BIB. I don't think they can. The window sliding open is what set OP in to commando mode. If OP and Reeva had just spoken in bed, then Reeva had to have opened the window when she entered the bathroom. So at that exact moment the clock starts to countdown - OP arms himself and slowly approaches the intruder and arrives in the bathroom and fired four shots; trouble is that in that same short time Reeva would have to move from the bathroom window that she had just opened, go in to the WC, empty her bladder, finish up, pull up her shorts, slam the door and lock the door. There just is not enough time for OPs story to be true.