Isn’t that confusing cause and effect? You’re getting interest because they’re paying it to you. They wanted to borrow, and even if there’s no risk, you won’t lend it out for free.
One might argue about the relative value of interest rates vs risk, but all lending incurs risk. Maybe very little, but non-zero.
Nonetheless, I think you can derive a “time value of money” from the data?
But as an academic exercise, you can stipulate risk free lending as axiomatic, and still see that a natural interest rate comes from different inter temporal marginal preference for money among entities in the economy. It’s only zero if everyone’s preference is identical.