How quickly can first release be rolled back to standard release on a user basis

I'd suggest something different, keep your main account as First Release in this instance, most or all of the time. Some of those changes that you might be looking for won't all light up at the same time but over weeks and sometimes months.  If your switching back and forth you may miss some of the nuances. To compare and contrast, I'd have a standard test account that I can use to monitor, particularly those features I am most interested in being widely available.  

For those SharePoint Developers/Architects, I'd perhaps split them, some on to First Release and keep a portion on standard release. This way they can as a group look out or track changes and promote new features for the standard users to look out for.  Just a thought anyway.

Just to add there is nothing with what you have suggested, I'd just possibly think it might be more hassle than it's worth.