Rehearsal time isn’t evenly divided across a piece.
I’d say that 75% of your rehearsal time will be spent on 25% of the piece.
That 25% might be phrasing, it might be tuning, it might be tempo, it might be pronunciation, it might be some really tricky bars. The specifics vary from piece to piece.
What doesn’t vary is that something will occupy a massive portion of your rehearsal time.
As a conductor, I try to anticipate what it’ll be, so that I can balance the challenges from piece to piece. (Not every piece is going to feature Croatian language work, for example.)
As a composer and arranger, I try to make sure that if I write something really hard, it’s balanced with things substantially more approachable. I might have an 8-part divisi section with rich harmony, for example, but it will be balanced with comfortable unison singing.