The best diving conditions at Tulamben are from April to November, during the dry season, when visibility on the Liberty wreck can reach 20 to 30 metres on good days. The wet season (December to March) brings more swell and reduced visibility but is rarely bad enough to stop diving entirely.
Tulamben is worth visiting in the wet season if you want lower prices and fewer people. The wreck crowds mostly disappear, and the dive sites are often shared only with resort guests. The sea here is generally calmer than the south of Bali even in the wet months.
Bali's high season (July–August and the Christmas–New Year period) brings more day-trippers to the wreck, which is why dawn diving is so strongly recommended. Book accommodation and dive packages in advance for these periods.