The official Governmental website number10.gov.uk states "Every Tuesday during Parliament, Secretaries of State from all departments and some other ministers meet in the Cabinet room in Downing Street to discuss the big issues of the day." ... "Mr Brown chose to move the meetings to Tuesday because Parliament does not meet until the afternoon that day, so members would not have to leave longer meetings early because of Commons engagements."
So I know the meetings are on Tuesday mornings, but not what time they start.
I've also Googled "cabinet meetings", "time of cabinet meetings", "when are cabinet meetings", "what time are cabinet meetings", "cabinet meetings uk what time" and other variants of this phrase, as well as looking on Wikipedia, cabinetoffice.gov.uk and direct.gov.uk.
Hoping that someone here is a civil servant or political journalist, because my (usually excellent) Google-fu is failing me on this.