I've just had a quick look at the rules and it does state specifically that they're looking for 60 or 90 minute scripts - so I'd suggest doing another draft before the deadline to fit it to the length they're asking for.
Finally, the Tony Doyle Bursary is looking for new writers; so I don't think having an agent would affect your chances of getting on the residential.
Throughout the year, the drama department looks for writers who want to write for Continuing Drama. Once a year, the Academy looks for writers who want to write for Continuing Drama.
It's no real surprise to find that some of the same writers are found by both searches, but it doesn't mean that being known previously increases your chance of being shortlisted.
The more likely explanation is that writers good enough to be shortlisted for the Academy are more likely to already be known by the drama department by one of the other routes mentioned above (agent, writersroom, theatre, and so on).
It's also worth noting that the presence of the second group of six (found by a previous Academy application) means that almost half of the shortlisted group this year were first discovered by their Academy applications.
We're going to be posting a bit more on non-Academy routes into Continuing Drama over the next month or so, so stay tuned for the details - but the quick answer is no, we're always looking for new writers and the Academy is just one way in.