Is a two-hour rehearsal on one piece too much?
Normally I think variation is a virtue. But I also think that some pieces need the concerted effort that can only come from laser focus. And honestly, I watched the clock spin in fast forward as we worked our way through a difficult piece today.
In the end, I think a solid balance of deep, narrow focus rehearsals and shallow, broad focus rehearsals is the best way to achieve your long-term goals.