Azure Content Safety and Content Moderation: Transaction limits

I am intending to use the Azure AI Content Safety and Content Moderation APIs for a project.

I'm trying to work out whether our use case fits within the limits of the Free F0 subscription tier.

I believe the free tier gives a permissible rate of 1 Transaction Per Second (TPS).  A transaction is a single API call.

My question is: over what period is the limit measured?  i.e. is the per-second rate measured over a minute, an hour, longer or shorter?  Perhaps someone can explain to me how the limit works as I am currently not clear about it.