I was on a 14 day British Isles cruise last summer. The first UK port will require a face to face immigration visit. This can cause hours of delay as the timing is determined by immigration officials, not the ship. Lerwick is frequently missed due to high winds (about a 50:50 chance of tendering). Edinburgh is slow if they are only using the ship's tender, but not bad if they are using local tour boats as well. The X99 bus can take you into Edinburgh from the cruise pier. My advice is to be ready to go ashore and at the tender ticket distribution site (usually BB Kings) when they start distributing tickets.