They never open them at all for about half the NFL games. The ones with point spreads of 3 or less, and 10 or more are the ones least often covered. This past Sunday was 14 games played Bovada had moneylines only only 7 of them.
Of the 7 they offered a ML on, 5 opened Friday night.
49ers/Cardinals opened Saturday night
Jets/Eagles opened only a couple hours before kickoff
College football from last Saturday can be
viewed here. Same deal ML on only some, missing quite a few every other site had odds for.