Food comps (Have/Have Not) is usually Friday - late morning BB time. (Usually don't have one after an endurance comp.)
Nominations are Friday late afternoon.
Veto comps are Saturday late morning (nothing in BB happens in early morning, they sleep til at least 9:30 most mornings.) Night vetoes are usually Friday night (after midnight actually, so they don't interfere with BBAD)
Veto Ceremony is Monday afternoon.
All times Pacific Daylight (BB time).
Like Puddin' said, though, the HGs always talk about the comps afterward, so you will almost always get spoiled if you watch the feeds.