git log --after '3 days ago'

Specific dates work too:

git log --after 2016-05-01

As with other commands and flags that accept a date parameter, the allowed date format is as supported by GNU date (highly flexible).

An alias to --after is --since.

Flags exist for the converse too: --before and --until.

You can also filter logs by author. e.g.

git log --author=author