How to stop the 3g on my iphone from turning off?

So i have an iphone 4 and i'm pretty sure its set so that the 3g turns off after 6pm. Is there a way to stop that from happening? I think its something my dad did

After 6pm, do you get a little moon icon next to your time? If so, go to settings, notifications, do not disturb, and turn off scheduled.

I'm not sure if that will fix it, it's the only thing i can think of. It could also be low signal