Avenir Or, increase the WW Battery setting a bit more e.g. to 10kWh, effectively all you are doing is increasing the charge rate. to meet your local need. The challenge as I understand it is that Giv. only fully accepts commands for certain values and modifies any request to meet its requirements and that may not completely match the % required/Time calculation so there always may be an anomaly, the trick is to adjust the WW system to give the desired result most of the time. Difficult for WW to do as there are too many possible equipment permutations but the user can tweak certain settings to meet their needs as in this case.
To give you an example here are my results (14.7kWh of batteries) over the last few days, newest at the top oldest at the bottom. My cheap period is a 7hr slot.
Start%/Requirement/Achieved%/Notes
3 100 100 bang on time
7 100 100 15 mins to spare
53 100 100 40 mins to spare
3 100 100 bang on time
6 100 100 Set WW Battery to 15kW
9 100 96 WW battery setting 14.7
28 100 98 WW battery setting 14.7