To find out all the files and directories including children ones that have last been changed or modified, use something like this:

Code:
find sampledir -mmin -40
Which prints out all files and directories in the sampledir directory that are modified in the last 40 minutes.

To get a list of files or directories that are changed in the last 20 minutes:

Code:
find sampledir -cmin -20
You get the idea. Read this post for differences of file change time and modify time.