Just my humble opinion, but I consider this a purely news-driven market until the folks in DC come to some agreement, and that agreement needs to include an increase in the debt ceiling. Once that occurs technicals will be back in play.
I think that tomorrow (Friday) we have a sell off, especially in the last hour, because many folks won't want to be long over the weekend. I don't think there will be a resolution during market hours Monday, but who knows after that. Typically we see some last hour agreement and if that was going to happen the buy-in day would be Monday prior to the deadline.
Many of us don't have a Sept IFT left and a last minute agreement would lead to a big up day tues OCT 1, which would be watched by us from the sideline. No last minute agreement would mean a pretty big down day on tues, and I guess I'd be watching it from home
So in my opinion the best buy-in day depends on when you think DC will come to an agreement.