with the cron format

* * * * *
| | | | | |
| | | | |
| | | | +---- Day of the Week (range: 1-7, 1 standing for Monday)
| | | +------ Month of the Year (range: 1-12)
| | +-------- Day of the Month (range: 1-31)
| +---------- Hour (range: 0-23)
+------------ Minute (range: 0-59)

my question is on the day of the month, what if cron is setup to
use 31, what will happen if the month let us say February or any other
month that only has 30 days? Will cron run of these months?

See some other comments on running scripts at the end of the month

crontab entry to run every last day of the month