If u have like an hps or mh light over 250 watts then you should probebly just leave the lights off cuz of the heat, idk how hot ur grow rom gets, but i left my plants for a week under a 42 watt cfl, they were probebly 6 inches from it, i gave them a good bit of water and when i came back the soil was pretty dry but the plants were fine and they grew a lot, i run my light 24 hrs a day for veg, but if u have an hps or mh thats a lot of heat and depends on ur grow space but if ur just leaving for 2 days they'll be fine in the dark. It might be a little confusing for the plants when they start making different hormones because of the extended dark period. They won't need much water, other than that ur just missing out on 2 days of growth. You can also replace a powerful, heat generating light with a cooler one that won't complicate things as much, and keep the plants far enough away so they won't grow to the light's hot air space by the time u get back.
maybe this isn't possible for u but just for the heck of it i'll tell u how macgyver would do it. If u have a cable box, one with a plug on the back, check if the timer in the box can turn on the tv too, if it does then u've got a timer u can painstakingly program it for when u want the light on or off.
