I think that zoo will be open on Tuesday (surprised to read that Łódź Zoo is closed that day). Zoo shouldn’t be busy because Poles traditionally spend this day in cemeteries. How many time you need to see all? It depends on weather. Zoo has only some pavillons open to public (Monkey House, two Giraffe Houses, Amphibian House (rebuilt after big fire in 2012) and Invertebrates House. Opole Zoo is the most beautiful zoo Poland (not the best – this is definitely Wrocław) but the best time to visit it is from May to September. Tour is guided good so you shouldn’t leave anything. You can buy new guidebook at cash desk. The most interesting are: good collection of primates, specially lemurs and South America monkeys (you can compare gorilla enclosure to this in Warsaw), nice South America paddocks, the only wolverines in Poland, the biggest group of potoroo in Europe, sea lions pool, common enclosure for maned wolves and howlers, new common aviary for several parrot species (I didn’t see it yet) all in a unitary style (zoo was completely rebuild after big flood in 1997). Have a nice day!