Is there any particular reason for the timing of your visit to Japan?
Is there something that made you want to come to Japan at this point in time?
「このタイミングで日本に来た理由」という事が聞きたいなら、下記の文章を使う事が出来ます。
Is there any particular reason for the timing of your visit to Japan?
Why did you choose this time to come to Japan?
What made you come to Japan at this time?
Is there something that made you want to come to Japan at this point in time?
What's the reason for the timing of your visit?
イギリス 
