The Sundial in Anistar City can only be touched when it becomes active between 8-9pm.
According to most Pokemon players around the world, this refers to 8-9pm YOUR local time, but this is technically incorrect as the game uses your devices' clock to work out what time it is.
So if you try between 8-9pm and it still doesn't work, have a look at the clock setting of your console or PC.
If you want to check out my YouTube video showing how to capture the Sundial in Anistar City, then have a look at my YouTube channel.
I have a bunch of videos of Pokemon X & Y, so please have a look.
Good luck Pokemaster!