The salesperson in me states that it is 'this minute!' The pragmatist in me notes that there are seasonality and reality considerations depending on what you want to purchase. These considerations are: Will this be a second home or a primary residence? If it is a second home in Park City will it be used just by you and your guests or will you be renting it out? Or is getting the best value all that matters? Or do you have a picture in your minds eye which is very specific and price is less of an issue?
The condominium season in Park City is early September to mid-December. This is because many of the condominiums in Park City are rented out during our high demand winter season. Most buyers (unless they wanted to pick up a unit which needed to be renovated) do not want to carry the costs over the summer without the larger rental income that the winter season brings. Conclusion; if you are looking for the best value in Park City and don't mind carrying the cost without the rental revenue, purchase late in the winter when owners realize they will close when the rental demand and income slows. I will caution you that due to the high occupancy it is difficult to get in some of these properties during the winter months.
A non-rental condominium purchase would be in the spring since sellers will not be looking for the greater amount of income in a short period of time which winter brings, also some projects prohibit construction (renovation) in the winter and many of the winter employees will be hitting the streets looking for their construction jobs to start again and labor will be over supplied thus keeping the cost of renovation to a minimum.
And if you have not heard it before 'most of us came for the skiing and stay for the summer!'