Conveying temporal meaning
When a condition is related to time it acquires temporal meaning. This is expressed by using specific conjunctions which normally occur in temporal clauses. Similarly to temporal clauses such conditionals may reflect three temporal relations between the clauses: simultaneousness, previousness and sequentiality.
The most frequent conjunction that conveys temporal meaning in conditional clauses is when. Its basic meaning is “at the time that”, yet its use in conditionals does not only bring about temporal connotations but also changes the probability value of the sentence. Let's compare:
 If my boss phones, tell him I'm ill.
 When my boss phones, tell him I'm ill.
The first example points simply to a possibility of the boss's phoning, whereas the second one reflects the speaker's certainty that the boss is going to phone. It also expresses the simultaneousness of the events described in the subordinate and in the main clauses.
The exact Polish equivalent of when is kiedy, which similarly to English combines temporal meaning and the feeling of certainty:
[2a] Kiedy mój szef zadzwoni, powiedz, że jestem chory.
When is commonly substituted with gdy or, especially in colloquial speech, with jak (the semantic content remains similar, yet the sentences become more conditionally coloured):
[2b] Gdy mój szef zadzwoni, powiedz, że jestem chory.
[2c] Jak mój szef zadzwoni, powiedz, że jestem chory.