Friday seems less ideal to me, being the end of the work week and perhaps managers/hr aren't too keen to open such emails.
There is the risk that notifications and emails will get buried over the weekend in other communications.
By this logic I feel Monday morning is the best time. Anyone agree/disagree?
EDIT: Am I over thinking this?
For submitting an application to a job posting, they generally just get collected as they come in, then screened all at once, so when you send it doesn't matter.