Is there a session timeout?

Yes, if you don't use YarakuZen for 2 hours, you will be automatically signed out.

"Keep me logged in" box on the login page is not checked by default.

If you check the box, the signed in period will be extended to one month. 

Company Admin can change the sign in time extension period in the "Keep me logged in time" section under Company Settings>Settings page. 

Default extension period is 1 month, but the settings can be manually changed from 1 day to 363 days.