Unable to change outlook calendar events default times when using Icloud

I run outlook 365 on laptop linking via icloud to my icloud calendar .

This used to work fine..everything syncs both ways.

Recently if I go in to outlook and create a new event, it will set the time for the event to 06:00 - 06:30 (which is the default event time frame and start of the working day in the options settings )

When I go to change the start time and end time of the event, it allows me to select the time in the drop down , but will not save the setting. This is using the classic version of outlook.

If I move to the new version of outlook, it works fine.

I have also have a pc with the same setup using the classic version of outlook and it works fine.

I have deleted everything , re installed outlook and the Icloud app and it still has the same problem .

I dont want to move to the new style outlook.

The only difference I can see is that the version of Icloud is 15.3.138 on the one not working but 15.2.157 on the one which does work .

Any help would be appreciated