10 gallon tank question

[82028]

We had a 10 gallon tank with a filter and heater and everything set up for a few years but recently my mom got a 29 gallon aquarium so she emptied her old 10 gallon. I am giving it to my friend for her betta fish (i already have another 10 gal for my betta so i dont need it.) But my question is, we are still going to use the old rocks and filter to set it up so do i still have to let it run for a few days before we add her betta? Or would it be safe to put him in there the same day?
thanks!

[Betta Fish Bob]

DEFINITELY let the water get right first!

Usually a couple of days is what I do to be safe, there is a nice post on it here somewhere, I will find it for you.