moondial riddle: how to activate/start it?

[Blook88]

hi everyone.

just found the graveyard which has the moondial riddle. the only think im able to do is click "investigate". then i only get a text sayng "you can see nothing".
do i have to do something else before unlocking the riddle?

thank you very much.

 

[Shrike675]

It's essentially a reverse sundial. Which means it only works at night.

 

[Blook88]

It's essentially a reverse sundial. Which means it only works at night.

thank you for your answer