Quote Originally Posted by Animeniax
Thanks guys. If I was saying this in a polite conversation with a sempai, would it be ok to use the "ta" form of kaeru? Isn't that for plain form or informal talk?

Also, if they respond that it's been a while, is it ok to reply "hisashiburi desu ne". Is this appropriate use of that term, or is the word more for <it's been a while since two people have seen each other?>
When using other sentences to modify nouns, the simple form of the verb is always used, like in the case of kaetta, which modifies toki. This does not make it any less respectful, and is in fact the correct way to construct the sentence.

Hisashiburi desu is generally said when the people talking have not seen each other in a while, but the word Hisashiburi actually means not having done something in a while. An example would be "Hisashiburi ni katsu sando wo tsukuttemimashita." which means "I tried making a katsu sandwich after not having done so in a long time." Of course, this sounds really formal because I intentionally completed the words to clearly show what I mean.