I wouldn't say we have specific intensifiers for this sort of thing. If I wanted someone to really grasp the fact that it was important that a task be done today and no other day, I would probably just make the word "today" a little louder than the rest of the sentence or perhaps break it into 2 very distinct and separate syllables. I might point my finger at the person or use some other pointed hand gesture as I say the word "today".
If I wanted to use extra words I might say "I want it done today. Not tomorrow. Not the next day. Today. Got it?" or something similar.