Promoters (and TV executives) can't schedule boxing matches at precise time unless, in the event of a quick knock-out in a preceding fight, they're prepared to have the audience twiddling their thumbs for a long time.
There are two title fights before Haye v Ruiz. (Groves v Adamu & Lynes v Olusegun). If each fight 'goes the distance' it will (including the pre-fight hype and post-fight interviews) take up about an hour or so. So you should be able to work out roughly the latest time that the big fight might start. But a couple of early knock-outs will bring the start of the Haye fight forward.
Chris