A typical DnB track will have an intro between 32 and 64 bars long. The breakdown can be anywhere between 16 and 32 bars long. The drop to the middle breakdown will be 64 bars long with some kind of variation in the track happening after 32 bars. The middle breakdown, again, being between 16 and 32 bars long. The second drop to the end of the track will usually be 64 bars, again, with a variation happening at 32 bars after the drop.