Meaning of “Byou de(秒で)”

“Byou de(秒で)” means immediately. Byou(秒) means second.
The literal meaning of this is ‘in a few seconds,’ but since it usually cannot be done within that time frame, it is better to understand it simply as ‘immediately.
This is a slang.

Example Conversation

A: I’m starving!
B: I will cook Byou de(秒で), so please wait!

A: おなかすいたー
B: 秒で作るから待ってて