If you have 6 hours or a half day to spend in Leith, there are a few suggestions to make the most of your time. First, you can head to the Royal Yacht Britannia for a tour which usually takes about 2 hours. It's a great way to learn about the British Royal Family and the yacht's history. Next, you can visit the Trinity House Maritime Museum which provides you with information about the city's maritime history and culture and will take around an hour to visit.
You could also visit the Newkirkgate Shopping Centre, a community-style retail area featuring independent shops, a food market and supermarkets, which is a great place to pick up some souvenirs, mementos or gifts, and will take about an hour or so. You could also head to the Ocean Terminal shopping centre which has a range of shops, a cinema and a variety of restaurants where you can sample some Scottish food.
If you have more time and an interest in art and culture, you could also visit the Scottish National Gallery of Modern Art which offers a range of exhibitions and collections, or the Surgeon's Hall Museum which offers exhibits related to medical history, both cover about two hours to explore. For those with an interest in religious landmarks, then the St Mary's Parish Church, built-in 1483, and the ruins of St Anthony's Chapel can offer something to see and take around 30-45 minutes to visit.
Finally, if you just want to spend your time outdoors, then the Leith Links park, a beautiful park with kids play area and skate park, are a great way to finish off your stay in Leith.