Depends on what needs doing,and all greens need coring at some stage,and what size core hole.a small core 1\8 inch with no top dressing or heavy scarifying can be played on in a week if the turf is growing ,but if a big tyne of 5/8 is used with a good scarify and laser level to light topdressing it could be out from 4 weeks to 8 weeks depending on how much sand is needed or how far the green is out of level and the right growing conditions depending on the type of grass you have