You've still got a while to go, she still needs to bulk up. Faster flowering plants can be done in 7 or 8 weeks, but mostly 10 or so. You're probably looking at around 12 weeks.
Once all the pistils start dying and going brown she'll be finishing up.
Also, keep those caterpillars away from your plants. They like to eat into the bud and it can cause bud rot.
With the marigolds, leave 1 or 2 flowers to dry in the pot and then open up the base, there are neatly stacked long black seeds that you can keep for next season.