Jakmile přijdu do kanceláře, hned zapnu počítač.

Jakmile means as soon as or once. It shows that one action happens immediately after another.

So in this sentence:

• Jakmile přijdu do kanceláře, hned zapnu počítač.
• As soon as I get to the office, I immediately turn on the computer.

Compared with když:

• když = when
• jakmile = as soon as

Jakmile is more specific: it emphasizes that the second action follows right away.

Yes, it looks like a present-tense form, but it comes from a perfective verb: přijít.

In Czech, perfective verbs do not usually express a true present action. Their present forms often refer to the future.

So:

• přijdu = I will arrive / I come (in the future sense)
• not I am arriving right now

That is why přijdu is correct in a sentence about a future sequence of events.

For the same reason as přijdu: zapnout is also a perfective verb.

So:

• zapnu literally looks like present tense
• but with a perfective verb it means I will switch on / I’ll turn on

In this sentence, both actions are understood as future:

• first: přijdu
• then: zapnu

This is very normal Czech usage.

Because do kanceláře expresses movement into the office.

Compare:

• do kanceláře = into the office / to the office
• v kanceláři = in the office

Here the verb přijdu involves arriving somewhere, so Czech uses:

• do
  • genitive

That gives:

• kancelář → do kanceláře

If you were talking about being located there, you would use:

• jsem v kanceláři = I am in the office

It is genitive singular.

The preposition do requires the genitive when it means motion into/to somewhere.

So:

• dictionary form: kancelář
• after do: do kanceláře

This is a very common pattern in Czech:

• do školy = to school
• do domu = into the house
• do práce = to work

Because Jakmile přijdu do kanceláře is a subordinate clause, and in Czech subordinate clauses are separated by commas.

So the structure is:

• Jakmile přijdu do kanceláře, = subordinate clause
• hned zapnu počítač. = main clause

Czech punctuation is stricter than English here. The comma is required.

Hned means immediately, right away, or at once.

It reinforces the idea that the second action happens without delay:

• Jakmile přijdu do kanceláře, hned zapnu počítač.

Without hned, the sentence would still mean something like:

• As soon as I get to the office, I turn on the computer.

But hned makes the immediacy clearer and stronger.

Yes, Czech word order is fairly flexible, but different positions change emphasis slightly.

The original:

• Jakmile přijdu do kanceláře, hned zapnu počítač.

is very natural.

You could also hear:

• Jakmile přijdu do kanceláře, zapnu hned počítač.

But that sounds a bit less neutral and may place more emphasis on hned or on počítač, depending on context.

For a learner, the original word order is the best one to remember.

Počítač is in the accusative singular.

It is the direct object of zapnu:

• zapnu co? = what will I turn on?
• počítač

For masculine inanimate nouns like počítač, the accusative singular is often the same as the nominative singular, so the form does not change.

Yes, you often can.

• až přijdu do kanceláře = when / once I get to the office
• jakmile přijdu do kanceláře = as soon as I get to the office

Both are possible, but jakmile stresses immediacy more clearly. It sounds a bit closer to as soon as than až does.

So if you want the idea of right after arriving, jakmile is an excellent choice.

Because both verbs are perfective:

• přijít = to arrive, to come (completed arrival)
• zapnout = to switch on, turn on (completed action)

Perfective verbs present actions as whole, completed events.

That fits this sentence well, because it describes a sequence:

1. I arrive at the office.
2. I turn on the computer.

If you used imperfective verbs, the meaning would change:

• přicházím = I am coming / I usually come
• zapínám = I am turning on / I usually turn on

Those would not work as well for this one-time future sequence.

It can often be understood as a habitual routine stated in a future-style structure: Whenever I get to the office, I immediately turn on the computer.

Czech commonly uses this kind of structure to describe repeated routines too, especially when the focus is on the sequence of completed actions.

So depending on context, it may mean either:

• On a future occasion, as soon as I arrive, I’ll turn on the computer
• or Whenever I arrive at the office, I immediately turn on the computer

The sentence is natural in both readings. Context tells you which one is meant more strongly.