The value string may be placed in quotes (single or double, but matching) to preserve leading or trailing blanks.
The value string is not parsed for environmental substitutions, thus lines like: PATH = $HOME/bin:$PATH will not work as you might expect.
Note that crontabs in this directory should not be accessed directly - the crontab command should be used to access and update them.
Cron also reads /etc/crontab, which is in a slightly different format. Cron then wakes up every minute, examining all stored crontabs, checking each command to see if it should be run in the current minute.
Clock changes of more than 3 hours are considered to be corrections to the clock, and the new time is used immediately.