It looks like I added a feature without documenting it here, where an axis has a tickFormat property. This allows %f to be used to see what the seconds are in "seconds since 2025-02-09T08:35", the units Megha has in her files. She'd like to be able to see both forms.
v2025a_9 has this property, but I forgot one last step, to avoid the resetting of the userTickFormatter object which formats the $H:$M!c$Y-$m-$d style ticks. I've put this change in and the next development release will have this.