In the interest of adding positive, logical feedback to those who are here looking to have their TID problems resolved, I offer the following RE TID failing in hours to days:
1. I think we can all agree we all have the same basic hardware, with differing memory amounts and carrier chipsets.
2. I think we can all agree we all have the same operating system, give or take a few 7.0.x versions.
3. I think we can all agree we all have different apps installed and running both active and in the background.
I think we can all agree we all have different results with Touch ID.
So, what's different between our collective experience?
1. Given H.W that doesn't fail 100%, it's not a H/W issue.
2. Given a good IOS install that has not failed to install properly due to a myriad of issues, it's not an IOS issue.
3. If, given we have setup our phones as a new device, stripped down to just IOS for testing purposes, and TID still fails after initially working fine, it's not due to third party apps. (I have done this when it failed for me, BTW, and it still failed)
So again I ask: What's different between our collective experience?
I think we should all agree there's basically two differences: our unique fingerprints, and/or how we register our prints initially.
An observation one can make with reading this and the other threads RE TID is, those who had as frustrating an experience with TID failing, over and over ad nauseam as I know I did, decided to modify how they trained and used TID, and found it to finally work.
If and when Apple makes a S/W change to work better with corner case fingerprints, one can adapt and use the feature, and put the issue to rest.