So my experience from the Rotterdam was that we had to meet at the pier for the tour. I asked specifically if we could meet up at the tattoo and the shore excursion desk said no.
We met at 6pm shore side and got stickers with bus numbers. We went to Edinburgh city center and got off the bus, walked pretty fast uphill to the tattoo entrance. It was about 7pm by then and surprisingly we had some free time until the tattoo started. You make your own way to the seats at your own timing. On the way back, you are to spot HAL staff holding laminated signs with a direction arrow and HAL logo telling you which way you are supposed to walk to the coach.