Laiti ningekadiria muda vizuri jana, nisingechelewa kufika kituoni.

Laiti means if only. It introduces a strong sense of regret, wish, or counterfactual thinking.

So in this sentence, the speaker is not just saying a neutral if. They are expressing regret about something that did not happen.

Compare:

• Kama ningekadiria muda vizuri... = If I had estimated the time well...
  → more neutral
• Laiti ningekadiria muda vizuri... = If only I had estimated the time well...
  → more emotional, regretful

The marker -nge- is used for the conditional / unreal idea. In this sentence, it helps express a situation that did not actually happen.

• ningekadiria = I would estimate / I had estimated
• nisingechelewa = I would not be late / I would not have been late

Together with laiti and the time word jana, this creates a past counterfactual meaning: the speaker is imagining a different past.

In English, we often use had ... would have ...
In Swahili, -nge- plus context often does that job.

Because Swahili and English do not match tense-for-tense.

English often uses:

• If I had estimated the time well yesterday, I would not have been late...

Swahili commonly uses:

• laiti + -nge-
• plus a time word like jana

So the past meaning comes from the whole sentence, not from a special separate pluperfect conditional form.

Here, jana tells you this is about yesterday, and laiti + -nge- tells you it is unreal/regretful.

ningekadiria can be broken down like this:

• ni- = I
• -nge- = conditional / unreal
• kadiria = estimate

So ningekadiria means something like I would estimate or, in this context, I had estimated.

About the verb:

• kadiria = to estimate, assess, calculate roughly

In kadiria muda, it means estimate the time.

nisingechelewa can be understood as:

• ni- = I
• -si- = negative
• -nge- = conditional / unreal
• chelewa = be late

So it means I would not be late or, in this context, I would not have been late.

This is a very common Swahili pattern for negative conditionals:

• nisinge... = I would not...
• usinge... = you would not...
• asinge... = he/she would not...

Because chelewa often needs an idea of what you were late for.

Here:

• kuchelewa kufika = to be late arriving / to arrive late

The infinitive kufika means to arrive.
So nisingechelewa kufika kituoni means literally something like:

• I would not have been late to arrive at the station

In natural English, that becomes:

• I wouldn’t have been late getting to the station
• I wouldn’t have arrived at the station late

Kituo means station, stop, or stand, depending on context.

When you add -ni, you get a locative form:

• kituo = station
• kituoni = at the station / to the station / in the station

So kufika kituoni means to arrive at the station.

This -ni ending is very common in Swahili for places:

• nyumba = house

• nyumbani = at home / at the house

• shule = school
• shuleni = at school

Yes, jana could move, and the meaning would stay basically the same.

In the sentence:

• ningekadiria muda vizuri jana

the order is natural and understandable: estimate time well yesterday.

You could also hear:

• Laiti jana ningekadiria muda vizuri...
• Laiti ningekadiria vizuri muda jana...

Swahili word order is often more flexible than English, especially with adverbs like jana.

Still, the original sentence sounds fine and clear.

Yes, but the tone changes.

• Kama ningekadiria muda vizuri jana, nisingechelewa kufika kituoni.
  = If I had estimated the time well yesterday, I wouldn’t have been late...

This is grammatical and natural, but more neutral.

• Laiti ningekadiria muda vizuri jana, nisingechelewa kufika kituoni.
  = If only I had estimated the time well yesterday, I wouldn’t have been late...

This version sounds more regretful and emotional.

So:

• kama = plain conditional
• laiti = regretful wish / if only

Yes. muda means time, and vizuri means well / properly.

So kukadiria muda vizuri means:

• to estimate the time well
• to judge the timing properly

A learner might also hear other natural expressions in similar situations, such as:

• kupanga muda vizuri = to plan time well
• kutunza muda = to manage time
• kuhesabu muda vizuri = to calculate time well

But kukadiria muda vizuri is understandable and works well in this sentence.

Yes, it is natural and understandable. But there are a few other ways a speaker might express the same idea.

For example:

• Laiti ningepanga muda wangu vizuri jana, nisingechelewa kufika kituoni.
  = If only I had planned my time well yesterday...

• Laiti ningekadiria muda vizuri, nisingefika kituoni nikiwa nimechelewa.
  = If only I had estimated the time well, I would not have arrived at the station late.

Your original sentence is good. The main thing it teaches is a very useful pattern:

• laiti + conditional verb
• followed by another conditional result clause

That pattern is excellent for expressing regret about the past.