If you have flowers only rule is that hive has enough food store to survive over one week. Then it is reason to wait that they get honey from nature.
Nowadays I have poured syrup straight in combs if food store is too short.
When I have just snow gone I need one month food store in hives. It is some 10-15 lbs or 2-3 full frames food per hive. The more food restrict brood area this time of year.
If I have 4 frames in hive, it is enough if they have one frame full of food.