Indeed AutoInvest does take the invested funds (manual or auto) during weekends, but it’ll process the orders once the markets open. Until then, any invested cash will remain in your pie’s cash (auto invested funds) or in your account’s free funds (if the investment is manual)
If your pie was recently created or updated and the value of the slices are close to each other, meaning that there aren’t many overperforming or underperforming stocks, the rebalance option won’t be applicable to your pie.