Cron Limits?

[ZaSz]

If I push a few cron jobs continuously every 6 hours forever, will that get me in trouble? They will just check the database then modify if a value is over a certain amount.

[Sex]

No, of course not..of course it depends on where you're running them.
But most likely no because the system uses jobs at intervals like that.
And many other websites do as well for backups and such.