It took me 3 days once to get the Spiked head and it could've taken even longer.. Nothing will help the chance of getting the head we want other than trying more times. Just hang in there next time! You will get them eventually. I've already had 4 generations with the parents being Rainbow and Spike, going to be fifth soon!

Jamie if they argue, you don't have to wait for them to finish you can interrupt them and get them to keep trying until it says "Trying For a Baby". If it isn't successful and the family is wealthy, it's good to use a doctor consultation to see if they need baby boost to have a baby. If this is the case, try using baby boost next time before they try again.