Currently there is not a splash page that creates a process gate where users must click I Agree to continue. The best option for now is to have your ToS on the landing page after logging in so users see them, but in the US this is method is less sure to create an enforceable agreement to the Terms of Service than an I Agree button or checkbox with button. Would also need logging for the last date they accepted the terms. This might also be useful for cookie acceptance or privacy policy, etc.

A nice to have would also be schedule the ToS acceptance button to appear on a schedule.