Can you say "within 90 days after"?

I understand that you can say, "within 30 days of receiving your application", but I am seeing more and more "within 30 days after your application is received". Is the latter grammatical?

I see no grammar issues with either of “within 30 days of receiving your application” or “within 30 days after your application is received”. I prefer the phrase “within 30 days of receipt of application” or “within 30 days of receipt of completed application”. The number 30 can be replaced by 90 without affecting grammaticality.

‘within’ and ‘after’ are both performing a similar function and therefore ... should not both be used in the one construction

While at first glance it may seem that using both of within and after is redundant, in point of fact using both words removes an element of ambiguity present in both of the other constructions. Although “within 30 days” is often interpreted as meaning “within 30 days after”, it can also be interpreted as “within 30 days before or after”. Typically, one interpretation or the other is obvious, and after need not be explicitly mentioned. The slight redundancy it introduces is unimportant. In short, add the word after or leave it out as you prefer.

"Within 90 days after" is preferable to "within 90 days of" because it more clearly states that the clock starts ticking the day "after" the triggering event date. Whenever I see "within 90 days of" I am unsure when the 90 days run out.