No need to display the rate per unit of time. Rather a small widget like a fixed bar that gets depleted as time goes on could convey a similar idea.

Well it's not the same really, because you don't show the payment rate, but rather how far into its lifetime a job post is. This I'd argue is even more relevant information than the rate. Plus if you access the section a different times a day o after some days you'll get an idea of the payment rate anyways.