Hi Chris,
Did you see if the bees had started working on the Flow Frames yet by noticing little wax deposits between the cells at the bottom of the middle frames?
Generally, the bees will only start working on the Flow Frames when they need to i.e. every inch in the below boxes is at capacity, there is adequate forage available (you mentioned you’ve had a dry period which could be effecting this) and thus the population is able to expand into the third box (Flow Super) to meet this demand.
If otherwise, you may just be harbouring unwanted empty space in the hive by keeping the Flow Super on and if so, it would be best to remove it until conditions make it suitable to return.
In terms of understanding if you should start feeding your bees and how much honey stores you need, local and experienced advice is best for this.