Sentence Error

[maccaroo]

I do not understand how this sentence is wrong. Please help.

We´ve been working on this for too long. It´s high time we will finish it.

[Raymott]

I do not understand how this sentence is wrong. Please help.

We´ve been working on this for too long. It´s high time we will finish it.

We've been working on this for too long. Correct
It's high time we will finish it. Wrong.
It's high time we finished it = It's about time we finished it. Correct.

[David L.]

If somebody says, "We've been working on this too long", it implies, 'we should have finished it by now."

Your next sentence starts: "It's high time.." : this means, in the context of your sentence, 'NOW is actually beyond the time when we should have finished it - but it's still not too late (if we get it done quickly)'
So, the reader of the sentence expects you to tell them, what action is to be done NOW, or very quickly. Instead, the sentence goes on:
'we will finish it'.
This is Future tense. So - 'we will finish it tomorrow/next week/some day'

As it is written, the meaning of the sentence is like saying: Quick, let's get it done quickly ...nah, no, as long as it gets done - let's just promise that sometime in the future, someday, it will be done - we will finish it eventually.

[maccaroo]

Thanks for the help guys.

Just one more quickie. Even though finished is the past tense of the verb. Is the sentence 'It's high time we finished it', still classed as the present tense?

[Clark]

Thanks for the help guys.

Just one more quickie. Even though finished is the past tense of the verb. Is the sentence 'It's high time we finished it', still classed as the present tense?

It refers to the present, let's put it that way to avoid debates on tenses and moods.

[Raymott]

Thanks for the help guys.

Just one more quickie. Even though finished is the past tense of the verb. Is the sentence 'It's high time we finished it', still classed as the present tense?

No, it's in the present tense, but it's subjunctive, which often has the effect of using a past tense form.
Eg.
If I am well, I will run the marathon.
If I were well, I would run the marathon.