Sure it is, in the iframe call you have the option to choose how often you want to rotate the banner. I am not positive about the js call and it is probably not possible with the straight html call.
The Iframe call works well, the js call slows things down just a little, but then it depends on where you are running adsnew from. If you are running on your own server then it may not be a problem. The iframe call works well with internet explorer and the newer versions of netscape.