I'd just search around on ebay. Search for Relay 110V, like Potter&Brumfield or such. Many of them can switch 3 Amps which is plenty for up to 8 canister filters. :smile: Prices are all over the place, but you should be able to get something for $2-4 plus some shipping. There might be electronics supply stores in your area that have them for similar money without the shipping, not sure.
The relay will have various contacts, and a schematic on the plastic housing which tells you which pins are which. So you'll just connect an outlet to the NC contacts, and plug your filters/pumps into that outlet.
The delay timer comes with a diagram that shows which components are used and how they are connected, but you don't really need it since it has convenient screw connections for the wires. There is a variable resistor which allows you to adjust the delay time from roughly 30 seconds to 5 or so minutes. You can change that range by switching out some of the capacitors, but it seem like it would work for your purpose.