I can complete the 2nd set of solstice armor after the event ends?

[Potatochobit Lv3 pwrd Next Form]

as long as I turn the blue armor to purple
I can complete it later after the event ends?

[Simbah]

The first purple you get after the blue ones are the Majestic Set. These CANNOT be completed after the event ends. So if you want to complete it, do it before next reset.

After you completed the Majestic Set you get the Magnificent Set. The Magnificent Set has another objectives to do to obtain the white glow. These objectives however CAN be done after the event ends. So after you get the Magnificent Set, you can do the objectives to get the white glow whenever you want