Time on market before selling?

[Maggie Smith]

Hello, 

How long should you generally let a house sit on the rental market before selling it? It's a recently redone house, we've lowered the price, tried to advertise more, fixed a few more things. We're using a property management company long distance. This was my primary house that we've moved out of, and based on several factors, the housing price is very likely to appreciate a good deal over the next three years. The area is getting attention and there are several developments underway, so it would be a shame to sell it at this juncture. However, I also don't want to keep paying for the vacancy every month. Would appreciate any insight!