Fates in a zone have pools they draw from, these pools are refilled every game day. Lower difficulty fates have higher occurances in the pool ie they have 2-5 Possible apperances in an game day. Higher difficulty ones have less usually only 1 possible appearance a game day. There is a cap on how many fates can be up at a time (coerthas is7). Each zone reques approximatly 55

Clearing the easier fates in the area will increase the odds of the one you want to appear by about 1.5% inthe hour for each one. Timed out fates also count twards this. My rule if thumb is if you can get to the other fate whith a sprint why not do it to increase your odds. It only takes about 15 seconds to do the 3000 dmg to get gold in the book fates.