Screen Time Customization?

i have two teenage children with iPhones and iPads. We have screen time established for each, set up to disable most functions of the phone from 11pm-3pm the following day (eg social media, YouTube, safari). Both kids want to use iMessage to text friends during the day, and that seems reasonable, so I set it to allow messages at any time. Unfortunately now one kid is staying up until 2am texting his friends. Is there any solution for customizing the shut off time for a specific app like iMessage? If not, could I layer a third-party parental control app on top of Screen Time without screwing up the Screen Time limits already established?