That photo won't be any good - it was taken two months after the event. Mrs Harrod might have left Bob's glasses untouched but she'd hardly be likely to leave the mail unopened. Sorry.
Still, knowing mail was delivered at 10.30am, give or take ten minutes or so....that gives us something to work with, doesn't it? The CL didn't come everyday, so Bob must have been in the habit of bringing his own mail in. I don't think the CL would have brought the mail in that day, after all. This seems to be what happened with her:
Arrives at Bob's just before Noon.
Knocks on the door. No answer.
Checks the mailbox for the key. It's not there.
Sits on the stoop, waiting, worried, for Bob to return.
It would have been a little odd for her to remove the mail from the mailbox when she saw the key wasn't there, knowing she'd have to sit on the stoop with a pile of mail in her hand.
If Bob brought it in himself....then we know he was around at 10.30ish, but that he didn't get time to open it. That narrows the timeline down. LE report states it was unopened.