It seems to be that way nowadays. Early in the fares, it was more open, and a few years ago too. But in recent times it seemed to be Tue-Thu departures (and often returns, I think), but if going via transcon, you can hope for a rearrange from AA on cancel (they tend to be earliest and latest ones available, and if you book second last one, they'll probably stick you on last flight, so you can argue that you're stuck arriving at past midnight), getting you to rebook on a Monday or Friday, depending on 24 hours. AA used pretty much open up lots of options if they retimed, but last time I tried, they seemed to have a lot more restrictions.