“Actually, now's not a good time.”

At work, you're working hard to prepare for a presentation that you're giving in less than an hour. A coworker comes by to chat about a problem that she's having with another coworker. You don't have time to talk to her about this, so you say:

Actually, now's not a good time.

actually

Use this to tell people something that's different from what they are expecting to hear, or unexpected:

Wow, this is actually pretty good.

Actually, I'm looking to switch careers.

Actually it's been kind of slow this week.

In the example above, the speaker says "actually" because people who work together usually listen to each other's stories or complaints all the way through. But in this case, the speaker has to interrupt her because he's in a hurry.

now's not a good time

This phrase means that you can't do something right now because you're too busy, too upset, you're not prepared, or some other similar reason.

"Now" is not usually used as the subject of a sentence. For example, it's incorrect to say "Now is 5 o'clock". Instead, you say:

It's 5 o'clock now.

"Now is good" or "now is not good" are the exceptions to this rule:

A: Hey, when do you think we can sit down and go over the budget?

B: Now's good.

A: Do you mind if I ask you a few questions about it?

B: Sorry, now's not good actually. Can I call you back later this afternoon?