The daily periodic reset happens at 11:59:59, is it possible to specify to custom time like Electricty tariff changes at 7 am?
That seems not for the utility meter, this is a once(?)-a-day change.
My 2cts: base your cost-utility meter on consumption * prix and make the price depend on time-of-day
It is possible to reset at times other than midnight, but only if you use yaml. Then you can define a cron pattern.
However, what you want to do is define two tariffs and switch between tariffs using a 7am time triggered automation. See the second example here: https://www.home-assistant.io/integrations/utility_meter/#advanced-configuration
This will create two sensors, one for peak and one for off-peak energy. While they switch which sensor is accumulating based on time, they still both reset at midnight if you have a daily cycle selected. This means you know how much peak and off-peak energy you use per day.