Ubisoft isn't exactly known for getting the PC version of their games out on the same day as the console versions. However, they are trying super duper hard to get the PC version out at the same day as its console versions.
Producer Lesley Phord-Toy:
"We’re always aiming to ship all our games on all platforms at the same time. I don’t have any specific news on the PC version of Assassin’s Creed Unity, but I do know we’re planning on shipping on all three [platforms]: Xbox One, PlayStation 4, and PC. I haven’t heard any news differently than that.

"It can be challenging. PC has a variety of different hardware configurations that you can’t necessarily predict. On a console you know what’s in the box. Every customer has the same configuration for the most part, and first-parties push firmware updates so everyone has what you’re expecting to have. PCs are nowhere near as consistent. So it can be extremely challenging to try and support as many of those permutations as possible.

"Like I said, Ubi has been very successful at achieving same-ship in the recent past, so we’re very confident that we’ll be able to do the same for Assassin’s Creed Unity."

Guys, they totally mean it this time!

Guys, really.

Really.