It’s only the AD user home directories in my case that are mounted on a HDD RAID array (/home/samba1/.local/share/containers/storage/volumes/homes/). I know that samba checks for correct permissions on every share on boot.
/home and everything else is still mounted on the system SSD.
Anyways thanks for the answers @mrmarkuz ! 
I will try to make systemd to wait longer, so there are no problems further on.
So the solution was setting both TimeoutStopSec=x and TimeoutStartSec=x
I set it to 500s, which is plenty enough. It started first time now.