DIAGNOSIS This is normal and not a defect. The '6 minutes' claim is for subsequent batches once the machine's evaporator is already cold. The very first cycle after being off or at room temperature always takes much longer.
FIX There's no fix because it's working as designed. Just be patient. The initial cycle involves cooling down the entire internal freezing mechanism from ambient temperature, which can take 15-25 minutes. You'll hear the compressor running the whole time. Once it makes that first batch, the following ones should come much quicker, close to the advertised time, as long as you keep up with demand.
IF THAT DIDN'T WORK If *every* batch is taking 20+ minutes even after several cycles, then you have a performance issue. Check that the room is cool enough (below 77°F) and that you're not opening the lid frequently, which lets warm air in and resets the timer.
HEADS UP The time to first ice is also heavily affected by the temperature of the water you start with. Using cold tap water will get you to ice faster than using room-temperature or warm water.