sigan gwanriga jungyohaeyo.

Literally:

• 시간 = time
• 관리 = management, control, or handling

So 시간 관리 means time management.

가 is the subject particle. It marks 시간 관리 as the thing being described.

So:

• 시간 관리가 = time management
  • subject marker
• 중요해요 = is important

The structure is basically Time management is important.

Yes, you can.

The difference is:

• 시간 관리가 중요해요: focuses more directly on time management as the subject
• 시간 관리는 중요해요: makes time management the topic, often with a slight sense of as for time management...

So both are natural, but they have slightly different nuance:

• 가 = subject focus
• 은/는 = topic, sometimes contrastive

It means is important.

The dictionary form is 중요하다. In Korean grammar, this is a descriptive verb (many textbooks also call it an adjective). So it behaves like an adjective in meaning, but grammatically it conjugates like a verb.

Examples:

• 중요하다 = to be important / important
• 중요해요 = is important

Many Korean words are made from a noun plus 하다.

Here:

• 중요 = importance
• 중요하다 = to be important

This pattern is very common in Korean. For example:

• 필요하다 = to be necessary
• 가능하다 = to be possible
• 안전하다 = to be safe

So 하다 helps turn that idea into a describable state.

Because Korean does not need a separate verb like English is in this type of sentence.

In English, you say:

• Time management is important

In Korean, 중요해요 already carries the meaning is important, so nothing extra is needed.

중요해요 is the polite everyday style. It is very common and natural in normal conversation.

Related forms:

• 중요해요 = polite, everyday
• 중요합니다 = more formal
• 중요해 = casual

So if you are speaking politely to someone, 중요해요 is a good choice.

A rough pronunciation guide is:

si-gan gwal-li-ga jung-yo-hae-yo

A few notes:

• 시간 sounds like sigan
• 관리 sounds like gwalli
• 중요 sounds like jungyo

So the whole sentence is roughly:

sigan gwalliga jungyohaeyo

Yes. That is also natural.

The difference is:

• 시간 관리가 중요해요 = Time management is important
• 시간을 관리하는 게 중요해요 = Managing time is important

So:

• the first uses a noun phrase
• the second focuses on the action

Both are correct, but the original sentence sounds a little more compact and general.

Korean does not have articles like English a, an, or the.

So 시간 관리가 중요해요 can mean:

• Time management is important
• The management of time is important

The exact feeling depends on context. Korean usually leaves that kind of detail unstated unless it really matters.

Yes. 시간 관리 with a space is the normal standard writing.

You may sometimes see 시간관리 in titles, headings, or less careful writing, but 시간 관리 is the safer standard form for learners to use.