This is a very interesting question. But I guess as the journals want to be professional than they should find reviewers fast. I’d say not more than 10 days.
It depends from journal to journal. I also find that in some journals, the timing of your submission may also be considered. Generally the review process may get shorter closer to the publishing timeline and longer the further. For example, if the journal is scheduled to publish in July, you might get shorter process time if you submit in May and longer if you submit in August.
Also, a gentle reminder after 10 days or so would not hurt.