Do I get up to a year to purchase AppleCare for my MacBook Pro 2018?

The following has information for the UK:

Mac - AppleCare - Apple (UK)

and

AppleCare Protection Plan for MacBook / MacBook Air / 13" MacBook Pro - Apple (UK)

or

AppleCare Protection Plan for 15" MacBook Pro - Apple (UK)

Also see the following from the above link:

(1) The AppleCare Protection Plan must be purchased within 12 months of the original purchase date of your Mac and provides up to three years of additional service options from the original purchase date of your Mac. The AppleCare Protection Plan benefits are in addition to rights provided by consumer law. For details, click here. Service coverage is available only for Mac and its original included accessories for protection against ℹ defects in materials or workmanship and (ii) batteries that retain less than 80% of their original capacity.

It depends on what country it is. In the U.S. it is AppleCare+ and you have 60 days. See the following from AppleCare+ - Mac - Apple

Purchase AppleCare+ with your new Mac. Or buy it within 60 days of your Mac purchase:

• Online (requires you to verify your serial number and run a remote diagnostic)
• At an Apple Store (inspection of Mac and proof of purchase are required)
• By calling 800-275-2273 (requires you to run a remote diagnostic and provide proof of purchase)

The year refers to the old/regular Applecare which is no longer available in the US. The new Applecare + is not available in most countries outside the US and you only have 60 days. That is for Macs; there may also be a difference for iDevices.

And, it does depend on your location, so unless you want to post that, there is no way to definitively answer your question.