I decided to try compiling Back In Time from source after figuring out the dependencies, and it seems to start up fine. However, even with no cron-related options enabled, it tries to use crontab and fails. Installing dcron doesn't seem to resolve this.
I created a package.yml based on the AUR https://aur.archlinux.org/packages/backintime/
It build fine, however it appears to be necessary to use cronie (or maybe also fcron, etc. I did not try that). Dcron does not work for whatever reason. I could only find people stating that they switched to cronie. With this, everything appears to work. Only the icons appear to be a little bit too large.
If you want to try, install cronie first and start/enable cronie.service
This has sat in accepted for inclusion for over a year. Clearly, there is a lack of demand for the inclusion of this software, nobody has stepped up to provide a patch, maintain it, and properly integrate it. Closing as a result. Feel free to reopen but only when someone offers a patch via our proper patch submission methods and volunteers to be maintainer.