If you miss a boss, you can still get a title. You need to visit all 7 bosses only to get the max title. If you miss one or a few, you still receive the rewards. If you want a top title but have no time to do the event, you'll need to wait for event to return.
Who invests more gets more. You can't do nothing and receive the top rewards.
@trapwhre02 Though boss is twice a day you can visit only 1 boss. To kill boss and get rewards you need to have a quest for it. That means you can't kill 2 bosses at one day. 2 times were added so players from different regions could have a chance to participate.