Lutalyse only works if the animal has a CL (Corpis Leuteum sp?). So, if the animal cycled just prior to you turning your bull out, by day 5 she should have a CL for the Lute shot to work. 2-5 days later they all should be in heat - IF they have been cycling. During the first 5 days, he will be breeding anything that comes in during those 5 days. If the bull had not been with them, getting them bred, the shot given on day 5 would NOT work on them because it was too close to their natural heat.
Oh, and it was not mentioned, you MUST put a heat tag of some sort on the heifers. Anything he breeds you do NOT want to give a shot to.