So you have your laptop with Windows 10 and you also need to run Ubuntu for some reason. Even if Ubuntu is the main OS, you may want to keep Windows around for the occasional system upgrade (Dell Update comes to mind for example) and software that runs exclusively one one of the two platforms (UCINET is such a program for me).
You are then faced with two problems:
- Default boot operating system
- The clock gets descynchronized when rebooting between the two operating systems.
StackExchange comes to the rescue. For the first problem you have to modify grub. I have chosen to make so that upon reboot, it will boot the previous operating system it did, unless I choose otherwise via the menu. I use the saved method from this answer.
For the second issue, there are a number of answers that usually involve tweaking systemd or the windows registry, but the easiest thing you can do is to ensure that the windows time service is started automatically with a delay.