In Too Deep

After a spell with split second resolves (or otherwise leaves the stack), players may again cast spells and activate abilities before the next object on the stack resolves.

Split second doesn't allow players to cast the spell it's on at times when they otherwise wouldn't be able to cast it. An enchantment with split second may still be cast only during its controller's main phase when the stack is empty.

If the resolution of a triggered ability involves casting a spell, that spell can't be cast if a spell with split second is on the stack.

Players still get priority while a card with split second is on the stack; their options are just limited to mana abilities and certain special actions.

Split second doesn't stop triggered abilities from triggering, such as that of Chalice of the Void. If one does, its controller puts it on the stack and chooses targets for it, if any. Those abilities will resolve as normal.

Casting a spell with split second won't affect spells and abilities that are already on the stack.