When I did peronamin + 2 half pero puddings it was 50 minutes and not 60 minutes (though it should add up to >=780). The reward was silver last I tried.
Also, all of the silvers I got were the smooth silver reward, rather than the rougher one. Not sure if relevant.

Edited this post since I mistakenly said peronamin + pero pudding at first, which is 60 minutes.