Wagsreed, welcome to TFP!
For me, historically, heavy leaf traffic has caused me to close by the third week in October.
BUT this year, I am getting a Dome enclosure and I am going to TRY to just stay open
Which is sort of crazy in Michigan...but we'll see what happens. The dome doesn't ship til next Thursday or Friday.
Last year, a poster up in Hamilton, Ontario, stayed open using some thermal techniques, without a Dome, until Jan 11th.
In his case, with his equipment being inside a heated shed, he found that leaving the pump off as long as possible preserved temp, then would heat in full throttle bursts.
In my case, if I decide the snow-deflation-pump-off-dome-roof cycle and heat bill makes it too rough come Jan/Feb, I will either just keep the dome deflated and drop my heat (but to well above freezing) and move the water OR go ahead and blow out the lines but leave the dome on as my winter cover.
The issue is heat cost and viability of staying open has a lot to do with your tolerance for high gas bills. Essentially, if you have a 266 btu gas heater that's 80% efficient, for example, it can only use about 2.12 CCFs an hour...whch in my area, carries a cost of about $1.50. So if you can recover degrees lost in a short time right before you swim, (eg right now I run heater midnight to 8 am) and leave the system still the rest of the day. With this method, my gas cost averages $12/day.
Here is mdrejhon's thread about his winter experiment:
FAQ: Cheaply Keeping a Pool Hot -- 90F,95F,100F -- How we ran till Jan 11th in Canada
Here's my thread of the experiment if you're interested:
Anyone Have a Winter Pool Dome - Ameridome or Others? - Page 2