I was with a provider this week and at the end discovered the condom had broken and was all bunched up at the bottom of my shaft.  Thinking back I believed this happened at the very, very end based on some of the sensation I had.  Once I realized this I got up and took a good shower with lots of hot water and soap while she cleaned herself up.  This is not a provider I’ve seen before, she is TER reviewed, not what I’d call top drawer but not close to a SW or something like that.  

My questions:
Is it ever worth asking her about her possible STD situation? Is an honest answer even possible to be worth the asking?
How bad is my risk here?  I’d guess that the exposure was probably less than 30 seconds, ,maybe 60 (if was really at the end as I think it was) does the time even matter?
What are the time frames? To be contagious? To be tested?
Should I re-test a couple of times?

And one last question.  I’m a once a month or so hobbyist.  Mostly with regulars but I travel and see various girls.   Should I be tested from time to time? If yes, how often?

I think it's always worth asking about STD's and no one should be offended if you do.
(although my ex broke up with me when i asked him about it, jerk!!)
anyway, you should ask her if she has a recent std test she could show you, i keep one handy and ready in case anyone ever asks.
I don't know for sure stats on your risk, but i would think any contact without a condom holds a risk.

I get tested every 3 months and if you see a different girl even once a month I would suggest that sort of testing frequency for you.