There are a few reasons why your heat pump might be heating outside the cheap tariff period:
Still in learning phase: If you recently started using Havenwise, it might still be in the learning phase (typically 2 days). During this time, your tariff isn't taken into account yet for the heating optimisation as Havenwise is still being calibrated.
It's cost-effective: It's sometimes most cost-effective to not completely turn the heat pump off outside the cheap moments in your tariff. Instead, the heat pump will operate at low flow temperatures and high efficiency to maintain comfort.
Time of use optimisation not enabled: In the settings page, time of use optimisation is not enabled. That means the heating will not be optimised for your tariff, but rather for a "low and slow" operation.
Response to an indoor temperature drop: If there's an unexpected temperature drop (e.g., from opening a door or window), Havenwise will activate the heat pump to bring the indoor temperature back up to make sure you're comfortable in your home.