DD only in Yr 5 at the minute but she's said that when she goes to secondary school she doesn't think she'll need the CM anymore but would be OK being at home till her dad got in. I only work p/t so it would only be 2 or 3 times a week but DH won't get in till 6:30pm.
Now we live in a nice area and are friendly with neighbours if there is a problem, etc. DD is normally sensible and there would be instructions about not opening the door, etc.
One of my work colleagues was horrified though when I said I was thinking about it. Next door let their 11yo DD be home on her own till they got in - they get in a bit earlier though - about 5:00pm.
I don't think I'd be so worried if it was only 90 mins, but she'd be on her own for 3 hours.