For those of you not still playing the ports, this was one of the new features added into the GBA port. It's essentially what the Competition Cartridge was, so you have to run through the levels as quick as possible. You get points for your time, for collecting and for killing baddies. It's a pretty fun experience, really. This thread is for discussion of best times, advice and so on.
At the moment, I'm working on getting S ranks for all levels. I have about 4 to go.