Really, length of time is not the problem. You can bake an hour or longer (and the finished product gets stronger the longer it is cured). The problem is temperature. Most home ovens are not accurate, and some will "spike" either in preheating or when the elements come on to reheat the oven. This is especially true of toaster ovens. You'll hear over and over that the best way to prevent burning of your projects is to follow these steps:
1) get an oven thermometer. Test your oven to see how well the oven dial and the actual temperature in the oven match up. Adjust until you know your oven is reaching the proper temp for the brand of clay you're using.
2) monitor the oven for the whole baking cycle. Be sure that your oven doesn't spike. If it does, you can help minimize the spikes by adding ceramic tiles or a pizza stone to your oven while baking; they "hold the heat" and your oven doesn't have to work as hard to stay evenly heated.
3) try baking under a foil tent or in a foil "oven in an oven" by clipping two foil trays together, one upside down on the other, to form a baking chamber.
Here's a link to the bluebottletree, Ginger Allman's fantastic site full of great info about all things PC: https://thebluebottletree.com/how-long-bake-polymer-clay/
I recommend visiting and reading her entire site.