The two ideas I've had for map picking would be:
Captains submit map picks the Wednesday prior to matches. This would allow teams to practice those maps prior to match time and would be less of a headache for admins. The downside is that if a drop or bench player is required, there is no leeway to cater to them.
Captains submit map picks on the Sunday prior to matches. This allows captains to cater more to a lineup that is guaranteed but may lead to a lack of preparation. This process can also be time consuming.
Vote for your preference so I can get an idea of where most stand on the issue.