Many people run a 24 hour schedule...but personally i think all living things benefit from sleep. They could most likely be fine when you get back...especially if you slowly increase the hours before you leave and then when you come back gradually bring them down an hour or 2 each day. Its the drastic ups and downs that will trigger hermies. But again you're in veg and those can handle more abuse.
But personally I'd pop down to home depot or any garden center and pickup a cheap timer...even Walmart has them if your in the usa.
Also they will need to be full on soaking wet right before leaving, and possibly reduce the airflow so they won't dry as fast. 👍