"When I have more time, I will study more."
Translation:Až budu mít víc času, budu se víc učit.
That is not a grammatical Czech sentence. You need the future tense "budu mít více času".
Když budu mít více času, budu se víc učit. - If I have more time, I will study more.
Conditionals work differently in Czech and in English. In English this is the first conditional so the first clause is in the present tense https://www.perfect-english-grammar.com/first-conditional.html
In Czech you will have more time in some future point of time so you need the future tense.
Also, there is a difference between Když and Až here. Až is temporal, když is conditional.
You can translate "když" as "if". You cannot do that for "až".
Here "when" is clearly temporal, so we translate that as "až".