idioms

hello, i need your help in explaining the phrase'" time will be the essence of this agreement" as i'm in the middle of a contract translation and got accross this phrase.or is it and idiom?
i would apprecitae your help to understand it in a better way.

[Tdol]

If something if 'the essence' of something, it is the key element, so time if the number one thing in this agreement.

[Mister Micawber]

Completing the terms of the contract on time is critical.

[bmo]

Time will be the essence of this agreement. Can I say it slightly different and still retain its meaning?

1. Time will be of the essence in this agreemnt.
2. Time will be of essence in this agreement. (Is this correct?)
3. Change "in" to "of" in both cases.
4. Is the following the best?
Time is of the essence in this agreement. (simple present)