What I expected to happen was...
The FallingSand entity would vanish after the "Time" NBT tag ticked to 600.

What actually happened...
The entity remained even after 600 ticks. FallingSand entities spawned with "Time" over 600 also fail to disappear immediately.

How to replicate:
1. Spawn a command block
2. Input this command: summon FallingSand ~ ~1 ~

{Block:"minecraft:stone",Time:580,DropItem:0,Motion:[0.0,3.0,0.0]}

3. Activate the command block
4. The FallingSand entity spawned should fly upwards, then disappear after exactly 1 second before hitting the ground. However, it does not.