Previous day's energy usage doesn't start at zero

Hi,
I'm new to Home Assistant, and am setting up some dashboards. My energy supplier is Octopus and I've downloaded Octopus energy via HACS. When I check in the developer tools I can see that the half hourly data retrieved via the Octopus API looks sensible and agrees with what I see on the Octopus web site.

- start: '2026-05-29T00:00:00+01:00'
end: '2026-05-29T00:30:00+01:00'
consumption: 0.118
- start: '2026-05-29T00:30:00+01:00'
end: '2026-05-29T01:00:00+01:00'
consumption: 0.199
- start: '2026-05-29T01:00:00+01:00'
end: '2026-05-29T01:30:00+01:00'
consumption: 0.112

However, when I setup a graph in my dashboard the day's usage never starts at zero. It's as if the data is offset by some time. My graph config, MPAN and meter number redacted...

graph: line
type: sensor
detail: 1
entity: >-
  sensor.octopus_energy_electricity_xxx_yyy_previous_accumulative_consumption
name: Yesterday electricity usage
limits:
  min: 0

Thanks, Steve.