Standard Showdown sustains the Magic ecosystem and keeps attendance up until the event cycle recurs.
For the player, it's a weekly opportunity to hone, evaluate, and experiment with their deck and adapt it to the metagame, both within your store community and Magic as a whole.
Reward that innovation. Standard Showdown is where the event path bends toward competitive: winning ought to matter, so focus rewards on the top performers.
You may schedule Standard Showdown any day of the week except Friday. (Events must recur on the same day each week.)