After my candy tuft plants finish blooming there appears to be green seeds left. Will the seeds mature better on the plant or can I cut them off and save to plant later?
It is always best to leave them on until they mature. This will ensure that they are viable, and will germinate.
This article will give you more information on the care of this plant: https://www.gardeningknowhow.com/ornamental/flowers/candytuft/growing-candytuft.htm
I live in Zone 9
Spring or fall is ideal for dividing and planting perennials. It should have about 6 weeks to get new roots going before stress from summer heat or winter cold hits. It is possible to plant in summer but extra precaution needs to be taken. Protect new summer plants from harsh sunlight by rigging up some shade for 2-3 days. This could be a paper bag attached to a stick, a box placed over the plant with the top and bottom open or another method, depending on what you have on hand.
Candy tutf plants will survive down to minus what degree?
They are perennials in zone 4 -8. Zone 4 is to -30 degrees F.
https://www.gardeningknowhow.com/ornamental/flowers/candytuft/growing-candytuft.htm
See above question
They will grow to some extent almost anywhere. They will be happiest when not exposed to extremes, constantly.
They will grow just fine in your area with proper care. This article will help: https://www.gardeningknowhow.com/ornamental/flowers/candytuft/growing-candytuft.htm
Oklahoma rain too too much this year! Been in the ground 4 months. I love the plant but it is fading fast due to too much water!! Will it come back next year?
When the blooms are spent, it's best to cut it back to avoid it going to seed. If the plant is showing stress from relentless rain, then it is a good idea to trim it back. I would trim it to 2-3 inches above the soil surface instead of all the way to the ground. If Oklahoma begins to dry out, the plant might put on growth and make a reappearance before fall.
This article will help you:
https://www.gardeningknowhow.com/ornamental/flowers/candytuft/growing-candytuft.htm