For data counters resetting we need a reliable solution, because what are posted here are not.
If I use the script with day testing and I put this one in Default rule, this solution will trigger on every restart on the day which we test in the script.
If I use the script without date testing, but with a Calendar item for 00:01 midnight and my phone is turned on at this time, everything work as expected. But if the phone is turned off and is turned on at 8:00 AM, in the Calendar rule, Advanced settings, Match after calendar entry we have only 59 min and 59 sec to match after and will not trigger. If I set Calendar event entry for whole day, again, the solution will trigger at every phone restart in this day. If I set the Calendar event for 8:00 AM and, for some reason, I have the phone on by whole night, we have 8 hours of possible data transfer not counted for the new bill.
So, my idea is to have a script which somehow will store a flag “Resetting in this day done” OFF / ON and at every restart in this day, the script will read this flag and if OFF will perform the data counters reset and put the flag to ON, else do nothing.