Si mañana tienes un hueco, vamos juntas a la oficina.

If you have a free slot tomorrow, let’s go to the office together.

Breakdown of Si mañana tienes un hueco, vamos juntas a la oficina.

• tener: to have
• un: a
• tú: you
• nosotros: we

Questions & Answers about Si mañana tienes un hueco, vamos juntas a la oficina.

Why is si used here, and why isn’t it followed by the subjunctive?

In this sentence, si means if and introduces a real, possible condition:

Si mañana tienes un hueco... = If you have some free time tomorrow...

After si, Spanish normally uses the indicative, not the subjunctive, when the condition is realistic or open:

• Si vienes, salimos.
• Si tienes tiempo, vamos.

So tienes is correct.

You would use a different tense pattern for more hypothetical or unlikely situations:

• Si mañana tuvieras un hueco, iríamos...
  = If you had some free time tomorrow, we would go...

So in your sentence, si + present indicative sounds natural because the speaker sees this as a real possibility.

What does mañana mean here, and where does it go in the sentence?

Here mañana means tomorrow.

It comes right after si, giving the time frame early:

Si mañana tienes un hueco...

That is very natural in Spanish. You could also move it, depending on emphasis:

• Si tienes un hueco mañana...
• Mañana, si tienes un hueco...

All of these are possible, but the original order sounds smooth and common.

A useful note: mañana can also mean morning, but in this sentence the context clearly makes it tomorrow.