هي توافق: ليس اليوم بل غدا.

Because the verb توافق already marks 3rd person feminine singular, Arabic can often omit هي. So هي is not strictly necessary here.

It is included for things like:

• emphasis
• clarity
• contrast with someone else

So both of these can work, depending on context:

• هي توافق: ليس اليوم بل غدًا
• توافق: ليس اليوم بل غدًا

توافق is an imperfect verb, 3rd person feminine singular, from وافق.

So grammatically it means something like:

• she agrees
• she is agreeing
• sometimes she will agree, depending on context

In normal unvocalized Arabic, you see توافق. In fully vocalized form, it would typically be تُوافِقُ.

Because the subject is هي, which is feminine singular.

Arabic verbs agree with their subjects in gender and number. Since the subject is feminine singular, the verb appears in the matching form:

• هي توافق
• not هي يوافق

The colon introduces the words that follow as the content of what she says, agrees to, or states. In modern Arabic writing, punctuation like the colon works much like it does in English.

So here the colon signals something like:

• what follows is the actual content
• the next part is being presented directly

It is a modern writing device, not a special piece of Arabic grammar.

Because the sentence is presenting the following words almost like direct speech after a colon.

Very often, وافق does appear with على when followed by a noun or idea, for example:

• توافق على الخطة = she agrees to the plan

But here the structure is different: the colon introduces the content directly. So the sentence does not need على in this form.

It is best understood as an elliptical sentence, meaning some words are omitted because they are obvious from context.

A fuller version might be something like:

• ليس الموعد اليوم بل غدًا
• ليس ذلك اليوم بل غدًا

Arabic often does this in short, natural replies. English does the same thing:

• Not today, but tomorrow.

So yes, it works naturally, even though some material is understood rather than stated.

Because ليس belongs to a new clause after the colon. It is not describing هي.

In other words:

• هي توافق is one clause
• ليس اليوم بل غدًا is the content of that agreement or statement

The understood subject of ليس is something unstated, such as الموعد or an impersonal idea like it. So ليس does not have to match هي.

If the omitted subject inside that second clause were clearly a feminine noun, then ليست could be possible in a fuller sentence.

Because ليس is very natural when Arabic is negating an implied statement such as:

• الموعد اليوم
• it is today

So ليس اليوم بل غدًا means:

• it is not today, but rather tomorrow

Using لا here would not sound as natural for this specific kind of correction. The pattern ليس ... بل ... is the standard and elegant way to say not X but rather Y in this kind of nominal or implied-copula structure.

Here بل means something like:

• rather
• but rather

Its job is to cancel the first option and replace it with the second:

• ليس اليوم بل غدًا
• not today, but rather tomorrow

This is different from لكن, which usually means but/however and introduces contrast, not direct replacement in the same neat way.

So after a negation, بل is exactly the word Arabic commonly uses for:

• not X, but Y

That is just the normal idiomatic way these time words are used.

• اليوم = today
• غدًا = tomorrow

In Arabic, اليوم is commonly used with ال when it means today, while غدًا is usually used without ال for tomorrow.

So this pairing is standard:

• اليوم
• غدًا

Both are functioning as adverbs of time (ظرف زمان), so in full vocalization they are typically accusative:

• اليومَ
• غدًا

In everyday Arabic writing, short vowels and tanwīn are usually omitted, so you often see:

• اليوم
• غدا

That does not mean the grammatical ending has disappeared; it just is not being written out in normal unvocalized text.

Yes. If you want to spell out the omitted idea, you could say for example:

• هي توافق: الموعد ليس اليوم بل غدًا
• هي توافق: ليس الموعد اليوم بل غدًا

These versions are more explicit. The original sentence is shorter and relies more on context, which is very common in natural Arabic.