Add sensor/counter value to the past (yesterday)

[glsf91]

I have a script which is getting a value from an external website valid for the day before today and calculates another value. This can only be done next day after 08:00 in the morning because the external value is not available earlier. Then I add this value to a custom sensor.
So far so good.

Only the calculated value is an average of yesterday. It will appear of course in the graph at the time it is added 08:00 in the morning next day.
Is het possible to adjust this time to a time at the day before?

Example: value added at 17 feb 08:00 should get a time of somewhere at 16 feb, so it shows up in the graph on 16-2 instead of 17-2.