Quote from essphowhere did you get this kind of information? I've been looking myself but couldn't find anything.
It's not said anywhere if that is what you are after. It comes from personal experience. I'm not even sure if you can drop under 5 stars once they have been achieved or is the percentage to keep it really 96%, could be very well be even just 90% positive ratings.
I've done CSGO & TF2 maps and L4D2 campaign and followed their ratings with great interest, just like anyone else would have. I found out that 250 ratings was kind of the limit to get that 5 star rating. Of course my maps have also some negative ratings, so i did the math and followed when they actually get that 5th and that limit was pretty much 250 as long as i had 96% positive votes at that time. My first CSGO map took 250 ratings to get that 5 star rating, so did the L4D2 campaign too. The 2 later CSGO maps and the TF2 maps i submitted seem to have 150 rating limit to gain those 5 stars.