Ref. No. 1249 Alif
In the name of Allah the most Gracious the Most Merciful
The answer to your question is as follows:
In the above mentioned case, you have to repeat the fast. Doing iftar mistakenly before time even by 2 minutes invalidates the fast; although there is no kaffarah in this state.
And Allah knows best
Darul Uloom Waqf Deoband