Regarding the wallet (win 10), when I see my stake rewards time is around 3 days, it count down to 2 days and sometimes 1 days then it suddently credited the stake rewards and jump back to 4 days or 3 days. I am not sure is it a bug or not, maybe dev can look into it
Your staking reward time will vary according to your weight relative to how much weight the total network has.
The more weight you have the lower the time, if the weight of the network itself increases, so will your expected reward time.
Always shoot to have as many x42 as you can afford, that way you will get a lot more staking rewards.