Here are the photos!

Not trying to be nasty, but I hope if you took cuttings it was from your own plant. I'd be pissed if someone just helped themselves to my plant (happened once).

It was on a college, but the landscapers rip them out every year in about a month.

Lol, must be nice to have so much money to spend (budget). Then yeah a single cutting, esp if you weren't greedy wouldn't cause much harm, though technically it is vandalism (been in a thread on that in many years past).

They had so many bushes that taking even 50 cutting wouldn't be noticeable.

I also never rooted hibiscus before. What would be the optimal temperature, and should I use a bag for humidity?

I can only say that tropical hibiscus is a bit slow rooting for me, I never use any hormones, and usually just put it in a shaded place and keep it moist for 4-6 weeks (till I see new growth). Being as I live in a warm humid area, I don't need to bother with any heat or humidity guards.

https://www.google.com/search?q=rooting+hibiscus&ie=utf-8&oe=utf-8&client=firefox-b-1

Thank you!

My area's humidity is quite low, so I'll probably use a humidity bag.

Humidity bag is a must. Warm roots. Reduce leaves to maybe three. Easy rooter.