If you want to do a good job & not rush, it is best to setup a proper holding tank for the fish. I use a 30 gal
rubbermaid bin for my redecoration. <That is also my QT/hospital tank.>
I fill the 30 gal
with tank water, move the fish over. I put the filter & heater (and some of the decor) in the bin. I ran that for 3 days while I re-did my main tank.
Once you have the fish settled, you don't have to rush in re-doing the main tank. You can swap substrate, move things around, etc. You have time to wait for the tank to settle before moving the fish back. <I have a spare Marineland HOT filter, so I ran that with a water polishing filter for 4-5 hrs to get rid of all the fine sand/ crud floating in the water. If your holding tank is stable, you can afford to wait a day or 2 for your main tank to settle out on its own.>