This questions comes up once or twice a week during the Spring and early Summer. Some will say to feed until they have two deeps of foundation drawn, or until they quit taking it, whichever occurs first, and some will say you are beyond the time to stop feeding and you should let them sink or swim on their own and re-assess in fall. If there is no flow, the 1:1 syrup should stimulate brood rearing which should increase your hive population to take advantage of a late season flow. I fed mine from new packages in April until they had 2 deeps drawn...which was mid-June. I had one that took twice as much syrup as the other, but the one that took the least syrup in Spring is now the strongest and packing a honey super with nectar (even after 2 splits)...so each hive is different, even with the same type of bees in the same location. But I also have a number of recent splits that I am still feeding because they are behind the curve and our main flow is over. You need to inspect and assess what it looks like they need. If they are just packing away syrup into the broodnest, you should stop feeding. But if they are still drawing foundation and have plenty of space for brood, than you may want to continue.
Put in your location so you can get better responses which are targeted to your area of the country...our honey flows in the Inland Northwest may not be the same as California, or the South or whereever you are located.