diff --git a/knowledge base/find.md b/knowledge base/find.md
index acb88f4..9c0d7a7 100644
--- a/knowledge base/find.md	
+++ b/knowledge base/find.md	
@@ -3,56 +3,140 @@
 ## TL;DR
 
 ```shell
-# change the permissions of all files and directories in the current directory, recursively
+# Change the permissions of all files and directories in the current directory,
+# recursively.
 find . -type d -exec chmod 755 {} +
 find . -type f -exec chmod 644 {} +
 
-# change the ownership of all files and directories owned by a specific user or group, recursively
+# Change the ownership of all files and directories owned by a specific user or
+# group, recursively.
 find . -type d -user harry -exec chown daisy {} +
 find . -type f -group users -exec chown :admin {} +
 
-# delete all empty files and directories in the 'Documents' directory
+# Delete all empty files and directories in the 'Documents' directory.
 find Documents -empty -delete               # recursively
 find Documents -maxdepth 1 -empty -delete   # non recursively
 
-# get the extensions of all files larger than 1MB
+# Get the extensions of all files larger than 1MB.
 find . -type f -size +1M -exec basename {} \; | sed 's|.*\.||' | sort -u
 
-# get all empty directories in a git repository (but not the repo's ones)
-find $PATH_TO_REPO -type d -empty -not -path "./.git/*"
+# Find files last accessed exactly 5 hour ago.
+find . -type f -amin 300
+find . -type f -atime 5h
 
-# find broken symlinks in the given directories, recursively
-find $DIR1 $DIR2 $DIRN -type l -exec test ! -e {} ';' -print   # posix
-find $DIR1 $DIR2 $DIRN -xtype l                                # gnu find only
+# Find files last modified in the last hour.
+find . -type f -mmin -60
+find . -type f -mtime -1h
 
-# get files by name, in numeric order regardless of the directory they are in
+# Find files created more than 2 days ago.
+find . -type f -ctime +2
+
+# Find all empty directories in a git repository that are not from git itself.
+find path/to/repo -type d -empty -not -path "./.git/*"
+
+# Find broken symlinks in the given directories, recursively.
+find dir/1 dir/n -type l -exec test ! -e {} \; -print
+find dir/1 dir/n -xtype l   # gnu find only
+
+# Sort files by name, in numeric order, regardless of the directory they are in.
 find . -type f -o -type l \
   | awk 'BEGIN {FS="/"; OFS="|"} {print $NF,$0}' \
   | sort --field-separator '|' --numeric-sort \
   | cut -d '|' -f2
 
-# print quoted file paths
-# %p is for path
+# Print quoted file paths.
+# %p is for path.
 find . -type f -printf '%p\n'
 
-# sort files by size
-# %s is for size
+# Sort files by size.
+# %s is for size, %p is for path.
 find . -type f -printf '%s %p\n' | sort -nr | head -50
 
-# get files which are executable but not readable
+# Find files which are executable but not readable.
 find /sbin /usr/sbin -executable -not -readable -print
 
-# get files which are writable by either their owner or their group
+# Find files which are writable by either their owner or their group.
 find . -perm /220
 find . -perm /u+w,g+w
 find . -perm /u=w,g=w
 
-# get files which are writable by both their owner and their group.
+# Find files which are writable by both their owner and their group.
 find . -perm -220
 find . -perm -g+w,u+w
 
-# list set-user-ID files and directories into /root/suid.txt and list large files into /root/big.txt
-find / \( -perm -4000 -fprintf /root/suid.txt '%#m %u %p\n' \) , \( -size +100M -fprintf /root/big.txt '%-10s %p\n' \)
+# Record set-user-ID files and directories into '/root/suid.txt', and large
+# files into 'big-files.txt'
+find / \
+  \( -perm -4000 -fprintf /root/suid.txt '%#m %u %p\n' \) , \
+  \( -size +100M -fprintf big-files.txt '%-10s %p\n' \)
+```
+
+## Time specifications
+
+Primaries used to check the difference between the file last access, creation or modification time and the time `find` was started.
+
+All time specification primaries take a numeric argument, and allow the number to be preceded by a plus sign (`+`) or a minus sign (`-`).  
+A preceding plus sign means **more than `n`**, a preceding minus sign means **less than `n`** and neither means **exactly `n`**.
+
+Accepted time information:
+
+- `a` for the file's last access time
+- `c` for the time of last change of file status information (creation)
+- `m` for the file's last modification time
+- `B` for the file's inode creation time
+  
+With the `-Xmin` form, times are rounded up to the next full **minute**. This is the same as using `-Xtime Nm`.
+
+With the `-Xtime` form, times depend on the given unit; if no unit is given, it defaults to full 24 hours periods (days).  
+Accepted units:
+
+- `s` for seconds
+- `m` for minutes (60 seconds)
+- `h` for hours (60 minutes)
+- `d` for days (24 hours)
+- `w` for weeks (7 days)
+
+Any number of units may be combined in one `-Xtime` argument.
+
+with the `-newerXY file` form, `find` checks if `file` has a more recent last access time (X=a), inode creation time (X=B), change time (X=c), or modification time (X=m) than the last access time (Y=a), inode creation time (Y=B), change time (Y=c), or modification time (Y=m).  
+If Y=t, `file` is interpreted as a direct date specification of the form understood by `cvs`. Also, `-newermm` is the same as `-newer`.
+
+```shell
+# Find files last accessed exactly 5 minutes ago.
+find /dir -amin 5
+find /dir -atime 300s
+find /dir -atime 5m
+
+# Find files last accessed in the last 3 days.
+find /dir -atime -3
+find /dir -atime -3d
+
+# Find files created in the last 1.5 hour.
+find /dir -cmin -90
+find /dir -ctime -1h30m
+
+# Find files created more than 4 days ago.
+find /dir -ctime +4
+
+# Find files modified less than 30 minutes ago.
+find /dir -mmin -30
+find /dir -mtime -30m
+find /dir -mtime -.5h   # gnu find only
+
+# Find files modified exactly 2 days ago.
+find /dir -mtime 2
+find /dir -mtime 48h
+
+# Find files modified more than 4 weeks ago.
+find /dir -mtime +28
+find /dir -mtime +4w
+
+# Find all files whose inode change time is more recent than the current time
+# minus one minute.
+find / -newerct '1 minute ago'
+
+# Find files owned by 'wnj' that are newer than 'file.txt'.
+find / -newer file.txt -user wnj -print
 ```
 
 ## Gotchas
@@ -60,10 +144,17 @@ find / \( -perm -4000 -fprintf /root/suid.txt '%#m %u %p\n' \) , \( -size +100M
 - in GNU's `find` the path parameter defaults to the current directory and can be avoided
 
   ```shell
-  # delete all empty folders in the current directory only
+  # Delete all empty folders in the current directory only.
   find -maxdepth 1 -empty -delete
   ```
 
+- GNU's `find` also understands fractional time specifications:
+
+  ```shell
+  # Find files modified in the last 1 hour and 30 minutes.
+  find -mtime 1.5h
+  ```
+
 ## Further readings
 
 - [How can I find broken symlinks?]