No, it's forced. I came home from work and there was pop-up window which I thought was the usual nag screen. It said my Windows 10 download was ready.

Except this one had a count down timer at around 54 minutes left. There was also an option "I need more time...".

I X'd the box closed and went on thinking whatever.

54 minutes later, in the middle of typing an email, the system auto rebooted and "Configuring Update for Wndows 10" screen came up.

I took pictures of it with my cell which are kind of blurry because it's hard to have a steady hand during a good WTH rage.