Counting down to an exciting event is a very abstract concept. For young children, most days are the same. They don't know about the days of the week yet and so they wait for an adult to tell them what that day holds.
To get a child EXCITED about something coming up, I suggest a paper chain. You know... those old school things you used to make leading up to Christmas (Christmas day was always a gold link in our house). At our house, we are counting down to when Daddy comes home. We have our paper chain up on the wall. Normal days are white. Holidays or special days are a color (St. Patrick's Day is green, Easter is blue, Memorial Day is red). Anytime someone is going to come visit, the day is yellow. The reasoning behind all of the days someone is to come visit being yellow is so that Timothy starts to associate yellow days as an exciting day when someone special comes to the house. This way the day that Kyle is coming home, Timothy will have some kind of understanding as to what will happen. This is also a good way to really start talking about holidays and teaching about holidays. Timothy now knows that green is a special color to St. Patrick's Day. Each morning we talk about our next special day that we are looking forward to (St. Patrick's Day) and then I tell him about who St. Patrick was, different symbols that are associated with St. Patrick's Day, etc.
If you have a child who gets nervous and anxious about change, a paper chain may be a good way for him/her to see when the change will take place. It also gives you an outlet to talk about it each day. You can use that opportunity to give your child language he/she needs in order to talk about how he/she is feeling.
What could you count down to? I love seeing our paper chain getting smaller and smaller!