About that long.How long is a piece of string?
True, but that's a specialized instance though. The advice I usually hear for bettas is to do the changes more often and keep them down to 50% at most. And its still not a 100% water change that's going to require moving the fish out of the tank and causing it way more stress than is needed for a simple water change.Actually alot of betta keepers need to do 90%+ every few days as alot dont use filters (bettas dont like the flow).
Giving oversimplified, incorrect information isn`t being helpful. I know what changes I need to carry out inrelation to my tanks circumstances, but this info is unlikely to be of help to the OP.Well given the wealth of information you just dispensed I'd say I was more helpful than you're being.