Your horse needs to have worked out in the new system, without a special event (e.g. spooking, bolting, fighting the jockey, etc), at 100% energy for stats to be generated. (This is so that we’re comparing like-to-like re: times.)
For a horse that has stats, you will click on Race Stats > Workout Stats, and see this table. If you hover over the “(11 days ago)” it will show the actual date.
Settings (the cog icon in the top right) > Website > Mode (dark). You can also play around with the different themes, though they’re all pretty similar. (Mine are Nord for light, and Night for dark, FYI.)