There is no rocket science involved here. Since going out on my own, Saturdays and Mondays are no longer as significant as they once were. I’m always working. As a result, I set up the defer folders not on specific days of the week but instead length of delay.
3 Hours
I use this one for something that comes in that I need to look at today but can’t look at right now. I use this more than you’d think.
1 Day
This one is my pressure valve. When I can’t get to it today but it is something I’ll need to deal with soon, it goes here.
2 Days
This one comes in handy when I’m waiting for something to happen. Quite often someone will ask me a question in an email and its not quite yet time for me to respond. I’m either waiting for another piece of information from someone else or haven’t had time to do whatever is needed to respond. Two days seems like the sweet spot to defer those emails. When it shows back up in a few days I usually have the answer or light a fire to get the answer.
5 Days
This is the one I use the least. In order for an email to fall into this box it needs to be both of low importance and low urgency. Things that I’m putting off five days usually get their own OmniFocus task but once in a while something falls into that area where it’s not worth an OmniFocus task and I still want to keep it in play.
Like I said earlier, there are apps that can accommodate these deferred emails or you can use a service like SaneBox. If the volume of email is giving you trouble, I’d recommend giving deferred email a try. I use it on my legal, MacSparky, and personal accounts and, at this point, can’t imagine going back. Also, if you'd like to learn more about email, I know of a pretty good book.