It takes a long time, really long. I've got the first response only 2 weeks after applying. Though you can probably start right with their automated test if you find one without wasting time on sending an application directly. The process is quite straightforward from there - a series of interviews and a meeting at office at last. The questions they asked me at the very first screening call was quite unrelated to a particular position as I get it.

Applied via their job listing website. Got a hacker rank test after a few days. Once I cleared that I had a call with one of their recruiter and after that got a mail telling "we have decided not to take your application any further". Some system-generated mail is not so clear or why. Tried to follow up with the recruiter but no response. Expected more from booking.com