In terms of second. I previously based time on vblanks,
Now i am unsure that method will maintain accuracy throughout development.
On NTSC, 3606 vblanks = 1 minute. (Yes, 3606. The NES and Super NES field rate is 60.0988 Hz, slightly faster than 60 Hz.) What are you trying to time? Or are you trying to make sure you don't miss an NMI that occurs during a long DMA?