Thanks for all the helpful answers.
I did discuss this a few CA attorneys, but most don't know specifics of the UCCJEA, much less answers to my questions, and only offered to research it for me. I haven't been able to find anyone who's actually handled an international parental abduction and knows what they're talking about.
I am really trying to find out if there are exceptions to that 6-month timeframe (tolling, as you mentioned). The UCCJEA, to my layman eyes, only seems to have very strict exceptions such as requiring the other state (country) to explicitly decline jurisdiction.
There is an extradition treaty in place, but parental abduction is not a crime in the other country.
Thanks for the note re. the UFAP/IPKA (IPKCA?) and Interpol notices - I will try that also. Do these require prior custody orders in place? If so, I'm back to the UCCJEA conundrum.