Swarm suffers from it being in part of the park far away from everything else. As a result people go there in the morning and simply dont return as they expect it to be a 45+minute queue. In reality by that time on a weekend the 2nd train has been added and the actual queue time is walk on. what should then happen is the advertised queue time should be dropped to 10 minutes but that suddenly means everyone comes over and its no longer 10 minutes. As a result from 2pm onwards the swarm island is often empty.
Stealth fluctuates a lot, often having a high queues before lunch as its near all of the food places. it sometimes (really depends on the rest of the day) has a peak around 3:30 to 5:00 ish as people do it as their last ride before leaving. After 5pm the whole park is dead and most things have short queues.