Can spoke j-bend be too long for hub?
There is way too much space! Tensioning the spoke is going to stress the bend into opening the angle and you risk several failures. The spoke may break at the bend. The spoke-hole will be ovalized or break open through metal fatigue. There's also the risk of the wheel going easily out of true.
Put a stainless washer on the spoke first before threading it through the spoke-hole to compensate for this lack of material thickness of the flange of your hub. It's quite a usual procedure.
I've mentioned stainless washers (with stainless spokes) because introducing another a different material may cause electrolytic corrosion