Dill and Coriander for Research Trials

I am a master's student in Entomology at Michigan State University in Lansing, Mighigan. My study involves comparing native plants with several non-native plants as pollen and nectar sources for beneficial insects. I am looking for both Coriandrum sativum and Anethum graveolens to plant in an open field in Michigan.
I will be collecting the insects that visit these plants when they are flowering. Because of that, I would like to get each of these plants to flower for as long a period as possible. I will have plants placed in meter squared plots, with 5 repetitions, so will need enough seed/plant material to adequately fill each plot. How much seed/plant material would you recommend?

For coriander you need between 2.5 grams and 8 grams to seed a square meter. The lower number is recommended for seed coriander and the higher number is for cilantro or fresh leaf coriander. Because you are focussed on flowers you can sow a little heavier in order to get a solid stand, so 3-4 grams a square meter should work well for you.
For dill the recommended rates for fresh herb and seed production is 0.9-1.2 grams per square meter. Again, in order to get a bit fuller stand you could sow a little heaver at say 1.5-2.0 grams per square meter.

I am pretty sure that C. sativum does not transplant well; does A. graveolens still establish if it is transplanted? Do you have any ideas on how to keep these plants in flower for as long as possible, and when you think they are likely to flower? I recognize that the phenology of all of my plants will probably be sped up a little more than if they were in the usual garden setting.

Both coriander and dill do not transplant well. When the roots are disturbed, the plants – if they recover from the shock – will bolt immediately and you won't get much of a stand. Any stand you get will be spindly and small. You should sow both items where they are to grow.
As for lengthening the flowering period, staggering sow dates might help. But then you need more plots which may not be appropriate for your experimental design. Another tactic is to "deadhead" (pinch off) the flowers once the petals fall off and the seeds begin to develop. I don't know if deadheading works on coriander and dill, but on many other species removing spent flowerheads before the seeds develop helps to spur on more flowering.