There are a lot of factors that influence when you should get aerial photographs taken. The first thing you should do when trying to figure out a good time for aerial photographs is think about what features of the house you want to highlight the most.
Many factors can influence the shadows and lighting that fall upon the property, so it is best to know which areas are the most important to be lit properly. Once you know the part of the house you want to highlight, you should figure out what time of day provides the best lighting coverage of that area.
There are many ways to do this, the homeowner might already know what time that part of the house looks the best, but there are also many great tools and apps you can use to figure out when you can get the best lighting.
Sun Surveyor is a great smartphone app for accurate measurements of the sun, but feel free to look around and use whatever tool works best for you. The key to good lighting is to find a time where the sun will be facing that area without creating harsh shadows. It also seems counterintuitive, but sometimes the best lighting actually comes on a cloudy day, because the clouds create a softer light that doesn't create harsh shadows.