Crack in new drywall joint
Cracks like that occur because of, 1) settlement, or 2) expansion/contraction. 

1) If the House was built in 1970’s, then it has finished settling. Unless there is some underground work in the area, like new utilities, new piling, etc. 

2) I suspect it’s expansion/contraction due to the joint compound being too wet. 

There is no need to “wait for it to settle and crack more”.  I’d redo it as Jimmy Fix-it has suggested.