This could be less a time issue than a size issue. As I recall, N900 records in MP4 format, which shouldn't have any real limits. AVI has a 2G file size limit, which with the given compression could lead to time-limit length issues. But MP4 shouldn't...

One issue you may be having is that it records in MP42, which is still relatively new. MPlayer and several other players have had issues with the format, since it's closed source, and not fully documented.