Yes, challenge events have been on the same schedule so far, but they’re the old school E&P challenge events, with only 10 stages and one day shorter (start on Thursday instead of Wednesday).
Having said that, in your position, I probably would not wait for the challenge event. 2* are not really worth levelling imo, so you need some 3* fast. Sure, you could wait for the challenge event, but it’ll hold you back for a couple of weeks, only to have a small chance at one of the event heroes… Probably not worth it.
Also, there are not many healers in PC… In fact, there’s only 1 4* healer in the entire game, and he’s a challenge event hero, so you want to get used to playing without a healer. Armor can help. I used Varvara instead of a healer in the beginning and now I use Bridget as a 4* Varvara, but I often play without armor as well and only attackers. So I wouldn’t advise on holding on to Cooper dearly and replace him with a 3*/4* blue ASAP, so perhaps it’s a good idea to do a Blue Elemental summon with your coins.
EDIT: Also, if you’re keen on getting a 3* healer, there’s only 2 in the game, and the best one of them is Blue (Dougal), so another reason to do Blue Elemental Summon