Can the pre-compost be buried in the same spot every time or does it need to be in a new place each time?
If yes, how far apart in terms of days can we bury in the same place, over and over?
Yes you can bury in roughly the same place each time. Many people do this over the winter. Keep in mind that during the colder months, the breakdown in the ground happens a little more slowly, so its beneficial if the area is big enough that you can bury two or three bins in it side by side, and you just alternate sides each time you empty a bin. This will allow a little extra space and time for the soil biota to break down the material between emptying your bins. Come springtime, wait for things to warm up for a month or so, and this area can become a good place to go to for healthy soil.