Entry number as Giveaway ending condition instead of time

I saw a similar idea in another thread today as a sidenote but I thought it might come in handy for some of us. What I mean is that instead of giving an ending time of your giveaway you will set a number of entries. If this number is reached the giveaway will end and the winner will be chosen. This way giveaway creators can choose the winning chance of the users.

As for me it has a more practical reason. I did three of four puzzles and I often I can't determine how hard they will be and this makes it difficult to choose a suitable time. There was for example one puzzle with only one solver (or atleast only one entry which is good for him but saddened me a bit). This way I can say as soon as 20 people who have solved the puzzle entered the giveaway the winner shall be determined.

I don't know how much effort this would take and the site is working well with the options that are there. Just wanted to know if people would be interested in this.