What is the correct time to cut down hibiscus & Mexican petunias?

In my opinion, and take it for what it is worth, it is far too soon for both.

You don't have landscapers, you may have poorly trained mow and blow service workers. They know very little, nor do they care, blooms are gone, Edward Scissorshand come out. They whack and chop clients landscape within an inch of the plants life. If they survive, it is a miracle. Most people don't know the difference. We are barely a month into summer and they performed a hard prune which is typically done in late winter or early spring, depending on your location. The plants probably just needed a good "deadheading" and they did not either know better (which they should), or just too lazy to do the job properly.

https://www.gardeningknowhow.com/ornamental/flowers/hibiscus/tips-for-pruning-hibiscus-plants-when-to-prune-hibiscus.htm

http://homeguides.sfgate.com/mexican-petunia-pruning-83709.html

Call them on it and see what they have to say. If they are apologetic, give them a second chance. Everyone deserves a second chance. Have them check with you before they start cutting down trees and shrubs. If they spin a web of lies, fire them and find someone else, preferably qualified. Go for someone licensed next time.

Sad! I trim mine all year - but the word is trim - not hack. But I give it a good trim in winter because it helps the blooms in summer. good news - it will grow back.🤗

Thank you to Naomie & Linda for replying to my concerns.