Thanks @arambaut - this is great. Since I believe ~ 50% of the diversity in the tree comes from sequencing errors, the TMRCAs would likely be even more recent - possibly pushing the interval towards the end of December. That means that the outbreak was detected almost immediately after the first case, which - given that this is flu season in China - is just amazing. Detecting an outbreak of pneumonia (similar to flu) of a novel coronavirus that fast is truly impressive.