No ...not exactly متى　Mata = When ? عندما 'indama = When / while / at a time متى تذهب الى المدرسة ؟ when will you go to school ? سأذهب للمدرسة عندما يحين الوقت　i will go when it's about time to go

there is no big difference the both give the same meaning and can be used in the same situations except that we can’t use عندما when we ask. the difference is in how we say the word after it like this متى تصل يغفر لك الله عندما تصلى يغفر لك الله the two sentences have the same meaning but the first sentence in the verb (يصل) there is a missed letter and that happen when we use (متى) and the verb after it ends with one of this following letters (و,ا,ى) and not always it is only when u take a time saying the last letter(i didnt know how to explain this part very good without talking)

hi 1- we used always متى when we ask a question about time for exemple " متى وصلت = when did you arrive ? ". 2- we used متى or عندما in the sentence when we want to inform, not ask a question. whith a condition ; we used متى whith a past verbs and عندما whith a future verbs. for exemple: call me when you listen my message إتصل بي متى سمعت الرسالة إتصل بي عندما تسمع الرسالة