Another way to check if they are taking in a decent amount of nectar is at their watering hole. While they are still using up stores they need water to dilute them. Once the nectar comes in you won't see them gathering water any more.

If it's a very good flow lots of bees will be fanning at the entrance in the evening to replace the moist air within the hive. But I am not sure if it's as obvious with an Open Mesh Floor.

Doris