When.. Well there is a radio station in Detroit (WRCJfm) and they broadcast Classical Music 7am to 7pm.. use it when they are classical.
(most parks have quiet hours.. Do not use it during quite hours.. Generally 7a-7p is ok Generally quiet hours are lik1 10 P to 6 or 7a.)
How long to run: Depends on size of battery bank, Size of converter and state of charge when you take your finger off the START button.
Thus I can not really answer, but try this,, Multiple converter rating by 90% (0.75) Multiply battery amp-hour (C/20 method) capacity by state of DISCHARGE (That's 100-state of charge so if 75% (state of charge that would be 25%) Divide second result by first
This is the number of hours to near full.
Add 2 hours
Why the math: Well the (State of charge * Amp hours)/charge rage should be obvious.. Why de-rate the converter 25%? Most of them taper off as the batteries fill so you never get full output.
IF your battery bank and converter are perfectly matched and your batteries are at half full six hours should be your result.
Home is where I park it!