.............snip.........I am not bothered about any honey this year, but think getting some extra brood frames drawn out will be advantages.............snip.................my other gripe is all the books I have read talk about when there is a "flow on". But none tell you how to tell if there is currently a "flow on" or not.
Only you know what melliferous plants are available to your colonies within their forage radius; each plant type will give pollen/nectar at particular times. You need to look at what is around you and observe your bees.
As you're not worried about honey this year I suggest you concentrate your efforts in getting all the foundation you can drawn, ready for next year.
Bees will draw foundation into comb for only two reasons: for brood rearing, or to store food; nectar, honey, or pollen and foundation cannot be drawn without a flow – real or artificial.
Fill your box with frames of foundation placed over a queen excluder during a flow. You can feed 1:1 sugar syrup continuously to get bees to build 20-30 frames of foundation into drawn comb. When a real nectar flow occurs, the bees might well stop taking syrup, but they will still use it at night or on rainy and no-fly days. After 6-7 frames of foundation have been well drawn move the undrawn frames into the centre and the drawn frames to the side. Then add a second box of foundation. When the combs have been drawn, filled and ripened they can be extracted and stored. if sugar syrup is stored in these newly drawn combs it can be kept for feed in the winter - or put in the freezer and used in nucs etc next spring.