AAirpass' instant upgrade fares book you directly into the upgraded cabin. There is no waiting game. However, these fares are not offered on every route. I don't see them on CLT-FRA and a quick check of a few INTL routes from DFW comes up empty too. I would NOT assume they offer them on your route or, if they do, will continue to do so long-term.

In general, AAirpass flights book into Y, J, or F with the exception of instant upgrades and plan ahead economy. On a standard 2 cabin domestic flight, IU books into A inventory. On 3 cabin transcon, IU books into D. Plan ahead Y books into H.

If an instant upgrade is offered on a given route, it is available to be booked anytime there is available inventory for sale, which can be monitored via Expert Flyer