Anything great than 6 months would be a buyer's market.Time to buy would have been back between 2001 and 2011 when people couldn't sell their houses due to the stigma of environmental issues (see last comment) and competition with nearby Cobourg, ON.How long will the current market dynamics last in Port Hope?

Try calling Peniel Environmental in Milford, NH I think that's what they specialize in

What was on the site prior to the hospital.Value is highest and best use minus cost to get there (Including knocking down building, environmental etc.) 

Make sure you perform due diligence on sewer, gas, water, environmental studies, etc....

He's been around literally forever and knows all the county environmental people.

Does the property have any environmental issues?

Avoiding major grading.City political structure that is conducive to reasonable subdivision map timing and conditions of approval.Market conditions that provide sufficient demand for lot sales and/or home sales to support the lot sales.No environmental issues, or toxic soilsNo biological issues such as endangered birds, bees, butterflies, salamanders, lizards, owls, or anything else that may be or could someday become endangered.No wetlandsNo blue line streams, or any involvement from the Army Corps of Engineers.No major flood control or drainage requirements.

If there aren't environmental issues, flood plain issues, etc you've found a unicorn!

Assuming no surprises (i.e. environmental issues, permitting issues, etc), you would most likely have okay cash flow from the start even if you did nothing. 

Also keep in mind taxes are likely to go up when the property changes hands.Since this is a gas station, you should look into the environmental history.