Hey @fefontana,
The format of the timestamps in the canvas workpad is a known limitation, and is being tracked here: [Canvas] Apply relevant Kibana advanced settings · Issue #37436 · elastic/kibana · GitHub
As for changing the format/orientation of the legends...it looks like support for this is being discussed here: [Canvas] Make it easier to style chart axes · Issue #44325 · elastic/kibana · GitHub. Following the conversation in that thread, I found a snippet that worked for me:
This won't be a drop-in fix for you, but it should serve as a starting point:
.flot-x-axis div {
white-space: nowrap;
transform: rotate(-90deg);
text-indent: -100%;
transform-origin: top center;
text-align: right !important;
top: 280px !important;
}