The options which apply to the lastlog command are:
-b, --before DAYS
-R, --root CHROOT_DIR
-t, --time DAYS
-u, --user LOGIN|RANGE
The users can be specified by a login name, a numerical user ID, or a RANGE of users. This RANGE of users can be specified with a min and max values (UID_MIN-UID_MAX), a max value (-UID_MAX), or a min value (UID_MIN-).
If the user has never logged in the message ** Never logged in** will be displayed instead of the port and time.
The lastlog file is a database which contains info on the last login of each user. You should not rotate it. It is a sparse file, so its size on the disk is usually much smaller than the one shown by "ls -l" (which can indicate a really big file if you have in passwd users with a high UID). You can display its real size with "ls -s".
Large gaps in UID numbers will cause the lastlog program to run longer with no output to the screen (i.e. if in lastlog database there is no entries for users with UID between 170 and 800 lastlog will appear to hang as it processes entries with UIDs 171-799).