Calibre version 2.36 64bit installed here on Win 10 with no restarts yesterday, I've done 3 Win 10, and 5 Win 7 remote installs this morning, they were all OK too. I do upwards of a dozen calibre installs a week, I have
never had a request for a restart after a calibre install - mind you I do ensure calibre's not already running, as I do with all application installs.
The only time I see a restart for anything (apart from WU) is when an install asks me if its OK to stop or restart something and I say NO.
My Win 10 system (SSD system drive) shows the desktop within a minute, I run 25 'start with windows' tray gadgets (some are standard - eg network centre), they take another couple of minutes to come to life - but that does not stop me starting my browser, mail client etc.
Just noticed the Win 10 upgrade took liberties with my date and time display settings
BR