Yes, you can stop turning now. Keep an eye on the humidity and once they pipped externally make sure it stays above 60%, so they don't dry out in the shells. I've recently done a bit of a staggered hatch (unplanned, don't ask!). The chicks hatched over 8 days, with the last hatchers being exposed to fairly high humidity and not getting turned at all during the last week, except when they got knocked around by the newly hatched chicks. They were all fine.
Remember ducklings can and often do take their sweet time hatching. I give them about 3 days from internal pip, 24 hours to progress to external pip, 24 hours from there to zipping and then another 8 hours to complete the process. That being said I've had a duckling take 4 full days once, so as gimmie birdies said above, leave them and let them do their thing. Good luck and have fun!