It's really easy, and I've done it several times....just have your hotel buy the ticket for you in Shenzhen. I do find that the ticket is way too expensive for what you get, but you get some of the cash back at a tax refund office. The ferry is fast, only 30 min or so, and only 30 min to get cleared and ticketed after that. I'd still leave a lot more time though, just to be safe. Shekou is a bit of a mess, and you'll need at least 30 min. You have to have proof of the plane ticket (which makes me think your friend won't be allowed??) - they check your ticket, to see if you have visas and such, and you get put into a line to clear customs. I always get here 30-45 minutes early and always barely get on the ferry.