What would be the crontab entry look like for a job that runs on the first day of every third month?
The following will run script on the 1st of Jan, Apr, Jul and Oct at 03:30
30 03 01 Jan,Apr,Jul,Oct * /path/to/script
Alternatively, but less obvious
30 03 01 */3 * /path/to/script
Will run every three months at 03:30 on the 1st of Jan,Apr,Jul and Oct.