Yes you can. Wire up your greenhouse and plug in your lights without a timer. But most plants, and certainly adeniums, are diurnal. That is: they need night and day. So you don't need 24/7 lighting. Fourteen hours of artificial light is typically enough. Some growers provide longer "on" hours, up to 18 hours maybe. I think 14 hours is enough and more than that, it starts eating into the amount of darkness adeniums also need.

Pagan

Thanks. I wasn't sure if adeniums actually need darkness. The use of light helps me maintain a nice temperature. I could probably then go for 16 or 18 hours.

It would be great for me if I could just leave the lights 24/7 because I won't need any heating devices for the dark period.

You can do 24/7 lighting, it's not generally considered ideal.

Like, Tomatoes do best in 14-16 hours of light, but if you do 24/7 lighting, will be comparable in growth to about 10-12 if exposed to more than 20 hours of light

On the other hand, there hasn't been a great study I could find on Adeniums to test optimal hours, so it's a bit of a guessing game, and they're not what people usually grow under grow lights.

Heck, Adeniums are weird, for all I know they could prefer 20 hours of light and suffer no ill effects from 24/7 lighting.

Since winter growth “extra” even modest improvement is fantastic, so I wouldn't sweat it. You'll still get more out of it than you would unpotting them and storing them in the garage.

If you are using HO T5 Florescent lighting. Do not count on them giving you supplemental heat. They do not give off enough heat to keep a cold room warm in ambient temps.

Metal Halides are the hot heat throwers, but use a lot of hydro. Have never used them myself.

Rick

I only use HPS lighting which is hot enough to keep the right temperature. Maybe I will try 20/4 or 18/6.