Curing ink is like cooking a steak. If you want a rare steak, you have a hot pan and quickly turn the steak over before removing the steak from the heat. A well-done steak requires a lower temperature for a longer time for the heat to cook through the steak.
As printers, we want all inks fully cooked. Achieve a fully-cooked ink with a conveyor dryer that has a long hood rather than a wide hood. The longer hood allows the shirt to cure for a more extended period. Typically, that time should be at least one minute.
If the ink picks off with your fingernail, then you have a rare steak. Thicker ink deposits (steaks) require more than one minute for the PVC ink to melt into the garment. If the ink doesn’t cook long enough, it cracks.