I applied in-person. The process took 2 weeks. I interviewed at H&M (London, England) in Dec 2016
Interview
it was ok, put through a usual interview where one interviews you and another person records what you are saying. It went allright, put through a trail the following week which i did not pass. Trail consisted of sorting out clothes, putting them back in the right place. I would recommend you watch tutorials on how to fold clothes quickly and scope out the H&M place so you have a rough idea of where items belong beforehand.
There was an extremely large pool of applicants, and I knowing someone who worked at the company helped get my resume to the top of the pile. I heard back a couple weeks later and went in for an interview. It was very standard and straight forward. If you speak clearly and positively, you'll do well. In addition to this, dressing well for the interview and knowing current trends is very important.
I applied online. The process took 5 days. I interviewed at H&M (Melbourne) in Oct 2015
Interview
it was a group interview, we took turns answering a few questions. then I paired up with someone and we have to tell two most interest facts about each other. later we did a mock unpacking and displaying of clothes on the table in two minutes. That part was pretty intense but just remember to keep calm and listen for instructions.