I'd place this visit as top priority to all visitors of Berlin. You could easily devote a full day to absorbing the artwork, artifacts and amazing architecture that makes up the museums on this island.
Bring a good pair of walking shoes, lots of energy, some water and perhaps a small lunch.
Lots of unexpected surprises and breathtaking exhibits to admire. If you have time to visit more than one museum, there is a ticket available for €19 each to allow admission to multiple museums, please note booking visit times in advance is recommended to avoid disappointment.