Hi again. Four days before you get a larger aquarium, you probably can do it if you do daily water changes and adding Prime. Keeping them in the 7 gallon long term is possible.
Here the AA article on cycling with fish
I just learned about cycling but I already have fish. What now?!
You can get good information on Goldfish here at AA. In fact there are a number of us.
Some people recommend bare bottom tanks. Others, especially that have plants do use gravel. Goldfish do like to root about in the substrate.
If you can siphon the water; then match the temperature and condition the water and put the new water in, the fish are not overly stressed. Usually they like the small waterfall.
Hope this helps,