I estimate it takes 20 mins to buy an ice cream in Japan. If it takes "half a day" that's (charitably) 12x (8-hour days), or (uncharitably) 24x (16-hour days).
If I estimate a month to build your feature and it takes me a year or two, you're not going to be very happy...
If I estimate a month to build your feature and it takes me a year or two, you're not going to be very happy...