Live Activities - countdown progress bar from custom position

Is it possible to create a live activity with a live countdown progress bar that start at non zero position?

scenario:
start time - 10pm
end time - 11pm
current time - 10:30 pm
I want to start a live activity that will show a progress bar between start and end times

progress bar would start at 50% with 30 minute count down, both updating live

current limitation:
setting chronometer: and when: creates a live progress bar, but that progress bar starts at 0% (or 100%)
adding progress: and progress_max: hijacks the progress bar to the correct position, but stops it from updating live