We (balena) are a remote company who have to do a lot of these kind of things - one of my colleagues wrote a nice post about it -
https://www.balena.io/blog/the-unreasonable-effectiveness-of...
https://www.balena.io/blog/the-unreasonable-effectiveness-of...
I've been struggling with an issue myself where I have a non-24 hour sleeping pattern. Does your system handle changing of timezones gracefully? It's almost like my timezone changes by 1.5-2hrs every day, and sometimes stressful days will completely throw it off.
Figuring out how to stay in sync with a 24-hour world has been a thorn in my side for ages and I think planning like you're doing would help me tremendously. (I actually clicked to read the comments on optiplanner to do something very similar to what you've been doing!)
So if go nocturnal you can shift your work hours to the night and the scheduler will try its best. But there is another constraint which is your colleagues work hours, your hours should have some overlap with theirs so that the schedule is "solvable"
It also supports the use of java.time, which means it supports LocalDateTime, OffsetDateTime, ZonedDateTime, and all other time related functionality that deals with implementing the insane intricacies of time for you. For example: if a shift runs from you 2:00 UTC to 10:00 UTC and employees from different timezones can furfil it and Daylight Saving Time changes for one of those employee's regions, you can write a constraint to detect that and avoid assigning the DST-affected employee that night.