Have you or can you schedule a successful group exercise program after 8:00pm?
I live, again I say we live, and also work as the organizer for the complementary fitness classes in our high rise building. We are located in a major city and I try to change up the "routine" classes regularly but have noticed many residents in the elevator asking we add more classes at post 8pm. Our 9 plus year experience has lent us to a very lax show at this time, has the industry changed and we missed it? Many of our one on one's take this time slot they pay and are committed... are we missing the later night exercise groupies that need motivation? Or is this just a conversation starter so we welcome them into the earlier time slots with out remorse....
I guess the best way to know your answer is "give it a try". It sounds like you might have a captive audience for that time based on your location and input you have received. Let us know the results!
Class Demo: This will help see if people will show for the class and if the class is appropriate for that time period.
Group Exercise Survey: This will help determine if people are interested in night classes and will also see what classes are of interest.
Paid Classes: This can be a small fee but will help keep people honest with attending class, mainly due to the fact that they are paying.
Some European cultures and Latin American cultures enjoy working out late.
If that is not the case, I'd distribute an interest survey form to determine who is genuinely interested.
As I am sure you are aware that when the summer time comes classes that late tend to be empty because folks like to be outside.
Another thing I would do is have them pay for all of their classes in advance, require that they reserve and have an cancellation policy in place which states something to the effect if you don't show or don't give 24 hours notice they will be charged.
Best to you.
Those classes can be highly instructor- and format-dependent.
I would first see what type of class people have in mind. If your survey gives you a very mixed bag of answers ranging from restorative yoga to hip-hop you may find it difficult. But if most participants have common interests, you may give it a try.
Have a minimum number required and see what happens
There are many "night owls' out there!