Bees will only build enough comb that they can support and tend to. Flows or feeding will encourage comb building, but the real driver is more bees. When you get a good generation of brood to emerge and join the ranks, comb development will take off to support the added population and future generations. I noticed with my hives it was good steady progress at first, nothing extraordinary. Once a couple cycles of brood emerged and the flow was on, they built frames like gangbusters. I had a medium hive body full of foundationless frames built out in about 2-3 weeks after the first box was full.
Lets let them do what they do best.