All three buckets have flowered, and now have strong stems and leaves. There is a little browning around the edges but no major damage.
I have added an 1" of compost to the top of each bucket, which resulted in compacting the soil a little after watering.
Estimated date to maturity is 80-100 days so I guess I will just continue to provide water and sun.
I am afraid to dig around and look for potatoes so at this point it is just a waiting game.