How long can fish go without oxygen?

mayb 2 or 3 days ,bt if u change water daily 20 to 25% and add few plant mayb it cn survive to ur luck bt nt l0ng and wnt hv a healthy life , even exciss of oxygen cn kill them so better hv a c0ntrol by use of valve .and always keep neon in group in odd n0 like 5 , 7,8 or 9 or m0re if u hv minimum 5 gall0n tank.feed twice a daily with flakes and live f00d like bloodworm and dephyne once in week .try to hv sand layer insted of pabels and hv heavy plantati0n ur neon wud live healthy fr years . Best of luck