Dnes mám hotovost, proto nemusím platit kartou.

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Breakdown of Dnes mám hotovost, proto nemusím platit kartou.

• mít: to have
• dnes: today
• muset: to have to

Questions & Answers about Dnes mám hotovost, proto nemusím platit kartou.

Why does the sentence start with Dnes? Does it just mean today?

Yes. Dnes means today.

Czech often places a time expression near the beginning of the sentence if it sets the scene for everything that follows. So:

• Dnes mám hotovost... = Today I have cash...

There is no preposition here. English says today on its own too, and Czech works the same way.

You could move dnes elsewhere, but the beginning is very natural:

• Dnes mám hotovost.
• Mám dnes hotovost.

Both are possible, but the first one sounds more like As for today...

What exactly does mám hotovost mean? Why not just mám peníze?

Mám hotovost means I have cash or I have cash on me / available in cash.

The noun hotovost specifically refers to cash.
By contrast, peníze means money in general.

So:

• mám peníze = I have money
• mám hotovost = I have cash

That difference matters here, because the second clause talks about not needing to pay by card. So hotovost is the more precise word.

What case is hotovost in here?