Master chocolatier Barry Colenso, who was commissioned to make William and Kate Middleton's wedding cake, was asked to create the replica in store at the weekend.
Mr Colenso said that the clock, which took days to put together, is 64pc dark Belgian chocolate.
"I wish I had weeks to create it," he told the Herald. "Because it is such a complicated thing, I started to make the elements at home and then shipped it over in pieces. I came over to Dublin and took lots of pictures from various sides and then went home to my kitchen."
The UK-based chocolatier, who is credited with bringing the Thorntons chocolate brand to fruition, said that he looked for inspiration from everywhere to make up the various elements of the intricate design.
"I scoured the toy shops and DIY shops to look for the different shapes," he said.
"To make the actual chocolate face, we've made a mould and for the arms of the clock we imprinted a mould into starch and then poured chocolate into that.
"I was looking everywhere for ideas, trying to find something that has that the shape.
"It will not be a perfect replica of the clock, but it will be 80pc accurate."
However, Mr Colenso would not reveal the exact details of the weight of the ingredients as shoppers will have the opportunity to guess the weight of the super-sized clock.
If they guess correctly, they will be in with a chance of winning a €1,000 gift card.
The clock will ultimately be donated to Temple Street Children's Hospital, where staff and patients can enjoy the oversized treat.
Children at the hospital will receive miniature versions of the clocks.
The chocolate clock is on display at Clerys until December 10.