It's been approved so I get over a million api calls a day. I paid the developer to approve it, I can't remember what he said exactly, but he submitted it and said something along the lines of a program to change prices and stock in the shop. But his english was really bad and it still got approved, so it's quite easy I think.
The limitation is the php file. The php file takes around 20 minutes to do 780 changes. So I run it 3 times an hour, i.e. 2,340 an hour or 56,160 every 24h.
You can't run multiple php files at once, because it checks the database to see if it's a 1 or a 0, and because they are not fast enough to change it to a 1 or a 0, they all end up doing the same product before the 0 or 1 changes to say one php file has already looked at it.
If I get my limits raised as planned (4 months time), and Amazon doesn't screw me over somehow on fulfilling my orders. Then I will look into solutions of doing more than 50,000 items in my repricer when I get there.