First, I don't know if I would want to start / stop my Internet connection with a cron job, because I may be doing something important, and losing my connection at a scheduled time could cause me to lose my work.
What I do to keep from losing track of time when at my computer is as follows:
I have installed a text to speech software called festival. festival can be downloaded from the University of Edinburgh. The URL is:
http://www.cstr.ed.ac.uk/projects/festival/
You can echo text to festival as:
echo "This is the text string I want to hear" | festival --tts
which pipes the output of the echo command to festival, and the --tts tells festival to treat this input as text-to-speach, and output it to the sound system
I have also created a few scripts which use festival.
One reports the system time each quarter hour using my sound system.
The other is a wrapper for festival so I can create scheduled reminders in cron as:
spkup "Time to get ready for work!"
I set the job to run 30 minutes before I must be at work for 5 consecutive minutes on all 5 days I work. It can be irritating, but I am never late for work.
I also use cron to run fetchmail each quarter hour to retrieve any email. This way, I do not have to run fetchmail as a daemon. I like running services only when I am using them.
If you open a terminal window, and enter:
man 5 cron
You will get the following information with more detail:
The fields in a cron command are as follows:
minute [0-59]<SP>hour [0-23]<SP>day of month [1-31]<SP>month [1-12]{or month name(s)}<SP>day of week [0-7] {0 or 7 = sun, or use names}
Any entry may be a <*> which means first-last
ranges may be used in the form 8-11 which is equal to 8 and 9 and 10 and 11
Lists may be used in the form 1,2,5,9 which is equal to 1 and 2 and 5 and 9
Lists of ranges are permitted as 0-4,8-12 which is equal to 0 and 1 and 2 and 3 and 4 and 8 and 9 and 10 and 11 and 12
ranges may be stepped through as 0-6/2 which is equal to 0 and 2 and 4 and 6
You may step through an entire range with */2 - for example, if you wanted to do something each 2 hours, you can use */2 in the hour field
Hope this helps,