If you're using frozen berries, it will take longer to bring the jam to a boil and take a little bit longer to reach the right consistency. Since the berries are frozen, they will have more liquid than fresh berries. It will take longer for the extra liquid to evaporate. If you're using a pot that isn't wide, it will also take longer, since the smaller the surface area, the slower the evaporation. For frozen berries, it should take around 45 minutes - 1 hour. For fresh berries, it will be faster. Start checking the consistency or the temperature of the jam at 30 minutes.