No, a bigger anode does not give less time for processing. It allows you to use a higher current which in turn reduces the processing time per liter but thats only if you choose to use the higher current. Some people don't so their processing time doesn't improve much, if any. Its all up to the choices you make.
Processing cold makes the highest quality colloidal silver. Using a larger anode (bullion bar) will easily allow you to move to at least 5ma, maybe a bit more, where you can make a liter of 20PPM in one hour cold, no stirring.
You could choose to heat and use stirring where you can now up the current to 15ma and make that same liter (but slightly less high a quality) of 20PPM colloidal silver in 20 minutes.
The bottom line is, if you're not in a rush (who is, ever?) just go cold, no stirring with a bullion bar at 5-8ma (whatever you feel comfortable with) and live with the time to finish and be happy you've made the best colloidal silver anyone on planet Earth can.
If you want to experiment by all means do but keep good notes and only change 1 operating parameter per run so you know if you break something, you know exactly what you did that broke it. You know what I mean.
This is all a big balancing act. Everybody finds a slightly different set of operating parameters they're happy with and thats fine because there is no single perfect answer - just a whole bunch of perfectly good ones. But there are bad ones too so you do need to read the literature and understand the operating parameters.