I think there might have been a change on the platform and I cannot find a way to manually log time for previous days. Suddenly, I only have the option to log time for today.
If I go ahead and also log the hours today, I'll be exceeding the max weekly contract hours for more than one client.
Since it is Monday the previous Work Week has just ended and the Work Diary for that week is locked. Manual time can only be added to the current billing period before the Work Diary is locked.