You could... but read on! You might be able to run the promotion with one entry form and choose winners on a daily basis on that form. We've had quite a few folks do that and have it work out well. The only downside to that is in order to announce the winner inside the widget, the giveaway must be completed and no longer running.
So if you were to use one form, you'd still be able to choose winners, but you'd have to announce them outside of the widget until the promotion is over. That way, when the giveaway is over, you have a collection of all the entries and will be able to choose the final grand prize winner if you liked.