I think you got plenty of satisfying answers but let me just confirm these as I live in Dresden and have been on this route plenty of times. The train is usually on time except when there are signal malfunctions on the route which can sometimes lead to up to ~30min delays (which wouldn't be problematic in your case). The only reason for a problematic delay would be a suicide attempt by someone on your track which fortunately doesn't happen too often but has happened a couple of times when some relatives of mine were traveling. In general though, the direct train shouldn't pose a Problem.