Isn't max forever over 10 minutes long?
I think it would work but it would likely be over the limit to upload here.
It definitely works, as I have one. I'm not sure if this goes over the 10 MB limit, but this simfile is definitely in one of the limits and is a little over 10 minutes.
Yes, possible to have 10 minutes. However, it will be categorized under the Marathon songs in StepMania... SM can have any much of time you want to make.
Not to mention parse time on load and song finish. The longer the file, the longer it'll be before the song comes up when you choose it in the song wheel.
On older systems, this can take upwards of nearly a half or full minute on really long files.