How can I get a log of all commits a month after/before a tag?

Question

I am looking for a command using git log in a way similar to

git log --pretty=oneline tag1...tag2

but I'd like to get a log of all the commits a month after a given tag, without having to explicitly specify the date of the tag in question. Something like

git log --pretty=oneline tag1...(1 month)

Same question for all commits one month before a given tag.

How can I do that?