Here is an explanation of the crontab format.
# 1. Entry: Minute when the process will be started [0-60]
# 2. Entry: Hour when the process will be started [0-23]
# 3. Entry: Day of the month when the process will be started [1-28/29/30/31]
# 4. Entry: Month of the year when the process will be started [1-12]
# 5. Entry: Weekday when the process will be started [0-6] [0 is Sunday]
#
# all x min = */x
So according to this your 5 8 * * 0
would run 8:05 every Sunday.
30 18 * * * curl URL >/dev/null 2>&1
30 18 * * * curl URL >/dev/null 2>&1
30 18 * 1 * curl URL >/dev/null 2>&1
30 18 * * 1 curl URL >/dev/null 2>&1
Position 1 for minutes, allowed values are 1-60
position 2 for hours, allowed values are 1-24
position 3 for day of month ,allowed values are 1-31
position 4 for month ,allowed values are 1-12
position 5 for day of week ,allowed values are 1-7 or and the day starts at Monday.
crontab -e for edit or add cron/scheduled job
crontab -l for show list