You should have a very good chance if you check the website regularly. I registered interest for the Everton game last week (having bought a ticket for the Crystal Palace game in June) and checked the website this evening and was able to buy one. I checked for West Ham out of interest and there is a very very small number of tickets available on the site at the time of this post, but no doubt there'll be tickets becoming available at different times in the next week or so. Previously I tended to get an email from the club if tickets became available, having registered interest, but I haven't been as inclined to get notification from the club in more recent times. So it's worth checking the website as much as you can.