When making a library digispark compatible you should target attiny85 generally. If you need very specific timing, you can check F_CPU == 16500000 - however please do note this is a lie - it only runs at that speed when the digispark boots off a computer usb port. When powered externally it runs at 16.0mhz +/- 10%
I'm trying to think up a good mechanism for calibrating the digispark in the future, so it can run with a more precise clock speed even when not powered by a USB connection.