[Koha] how to make work of cronjobs ?

[SATISH]

Hi,
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Koha version -16.5.01 (upgraded from 3.16.00)
OS: Ubuntu - 14.04 server edition (upgraded from 12.04)
Install method - Packages
Postfix - working successfully.
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I am not sure how to set up and make necessary modifications in cronjobs
and need your help.

Our library works from 9:30 am to 5.30 pm on week days and 9:30-1:30 pm on
every saturday. (Desktop machine) as server, will be shutdown in the
evening everyday until library receives a dedicated server machine.

preliminary set up:
1. In System preferences >EnhancedMessagingPreferences > is set to Allow.

2. Each patron, is enabled to get  check in, checkout, overdue notices.

3. # crotab -e, shows, all lines are commented.

4. Is it required to run even for packages install method ? or is it
already setup?
  # ENVIRONMENT:
     PERL5LIB=/usr/share/koha/lib
     KOHA_CONF=/etc/koha/koha-conf.xml
(http://kohaworkshop.pbworks.com/w/page/7060237/koha%20cronjobs)

5. /usr/share/koha/bin/cronjobs shows -  crontab.example and it has all the
required instructions.

6. currently, after setting up postfix, overdue message, advance due
notice, check in, check out , new registration  notice all are working,.
but I wanted to properly setup timings as per our library's open and
closing hours.

Should "crontab.example" file be renamed ? or copied to crontab ? or how to
use this file ?

Kindly share your best practices?

with thanks
Satish MV
Librarian
Govt. Engineering College, Hassan
Karnataka.