this is why whenever I have a grow going.. I make double sure that I don;t have any upcoming events or plans that would cause me to have to leave for an extended period of time. I mean, if your only going to be gone for 2 maybe 3 days (example: leaving for the weekend) your ladies will be just fine. Just make sure you water them really good.. right before you leave. This way, you know you watered them right before you left to go wherever your going.. so you know they got watered.. you know you'll only be gone for 2 maybe 3 days at the most.. also make sure that your timer(s) are correctly set and working properly before leaving town. Don't want any light malfunctions while your gone.. that would be worse than if the plants never got watered. Cannabis is a 'weed' (no pun intended) - therefore it really doesn't need a lot of water to begin with. I generally water my ladies once every 3 or 4 days.. but what I do personally is I will also wait until the top layer of soil is completely dried out, between each watering. If you'll use that 'general rule'... you'll never have to worry about over-watering your ladies again.
But anyhow, yeah.. as long as your not going to be gone for more than 6 days, your ladies will be fine on their own. But like I said, just make sure you make yourself a checklist, that contains the things you need to do right before you leave town.
1. Water your plant(s) good enough to where you see water drain out the bottom (kinda like a very very light flushing.. as if you might have over fed and need to flush out the excess nutrients from the soil).
2. Check all bulbs and timers and make sure their in good working condition and working properly.
3. If its been a while since you have fed them nutrients.. or if your 'feeding day' falls on a day when you'll be gone.. go ahead and lightly feed them with nutrients.
Follow those three 'rules'.. and your plant(s) will be just fine for up to 5 to 7 days. Anything longer than 5 to 7 days and you more than likely will run into some kind of problem or problems.
Hope this helped ya out some..
peace.