@pschwede No it isnt that, IMO I think its fine if the system is imperfect a bit. I just figure it should work well enough that the output is somewhat meaningful. Having a week interval means most of the highest scored posts would never reach the target.

So how about this as a way to solve it that is minimal effort on your part but still ok..

Pick two intervals the first being shorter than the other. You can pick whatever makes sense to you but lets pick one day (We will call this I1) and one week (we will call this I2).

At the end of every I1 cycle (every day) pull up all posts that were created based on this formula (Today - I2) to ((today - I2) + I1). Of those posts that meet that criteria tally the score for each post (this score will be accumulated over the I2 period so it is a weeks worth of likes). Then rank the top post of those. Repeat this every I1 (every day).