You can do your drawing whenever you want, at the last minute or prepare in advance, the choice is yours.
If you are using Social Media Picker and you want to prepare your draw in advance, you must still wait until you have published your contest on social networks. Once your publications are online, you can prepare the settings of your print by selecting the publications and then the filters you want to apply. Once the settings are saved, your drawing will be put on hold in the “queued giveaways” category and you will be able to come back to it when you want to draw the winner(s).
If you are using Contest and you want to prepare your draw in advance, you can easily do so. Contest offers the saving option which means you can start adjusting the settings to your contest and come back to it later. Once the settings are saved and you are done preparing your draw you will be able to come back to it when you want to draw the winner(s).