Urgent

Rahiil: to improvise means to use whatever you have rather than use exactly the right materials or to change plans as circumstances change. While improvising is often done to save time, it doesn't always mean that it needs to be done right away. To improvise is also a verb, not an adjective.

Svetlana: your words/phrases are closer in meaning to what Maria Eugenia requested, but they're adverbs and adverbial phrases, not adjectives either. 

it must be done : immediately

                         right now

                         right away

                         as soon as possible

                         at once

and I m sure there re far more ))))

Improvising means do everything as soon as possible

Without anty hesitation

Many adjectives can be in English

I think every synonym of rush and .....can be use 

Thanks a lot, Mike :-)