IMO every team should be aiming to run 2nd half races for junior riders, let riders book in advance so they know they're guaranteed 2-3 rides. Obviously major incidents or bad weather will impact on the time available to run the races, but if meetings started at the advertised time, no delayed start due to queues outside, unless a major RTA in the area. If everyone knows the parade is 7:15 and first race 7:30 its upto them to get into the stadium ontime. Barring major incidents or poor weather it should be easy to get 15 races done and dusted in 90 minutes, leaving a fair bit of time for some junior races.