When the Boston Symphony Orchestra’s conductor announced on Tuesday that his herniated disc would need immediate operation, they didn’t know what they were going to do. Daniele Gatti, the temperamental Italian conductor, was brought in, instead of going with a local Boston assistant, because the orchestra wanted someone special for the opening of the season. He was surprisingly good, considering he hadn’t practiced with the orchestra until just a couple days ago. The critics are pleased with the way the orchestra performed with him, and there were only a few points that they would have improved on first glance. Not bad for a 3 day rehearsal sequence. To be fair, the music was all familiar to the musicians and the conductor, so we don’t need to think that they were improvising. But still, getting everyone on the same page is very tough!